U.S. patent number 5,244,762 [Application Number 07/816,994] was granted by the patent office on 1993-09-14 for electrophotographic imaging member with blocking layer containing uncrosslinked chemically modified copolymer.
This patent grant is currently assigned to Xerox Corporation. Invention is credited to Cindy Chen, Raymond K. Crandall, Steven J. Grammatica, Joseph Mammino, John W. Spiewak, Robert C. U. Yu, Huoy-Jen Yuh.
United States Patent |
5,244,762 |
Spiewak , et al. |
September 14, 1993 |
Electrophotographic imaging member with blocking layer containing
uncrosslinked chemically modified copolymer
Abstract
An electrophotographic imaging member including a supporting
substrate, a charge blocking layer, an imaging layer including at
least one photoconductive layer, the blocking layer including an
uncrosslinked copolymer derived from vinyl hydroxy ester or vinyl
hydroxy amide repeat units chemically modified at a nucleophilic
hydroxyl group by a monofunctional electrophile, the copolymer
having a number average molecular weight of at least about
10,000.
Inventors: |
Spiewak; John W. (Webster,
NY), Yuh; Huoy-Jen (Pittsford, NY), Mammino; Joseph
(Penfield, NY), Yu; Robert C. U. (Webster, NY), Chen;
Cindy (Rochester, NY), Crandall; Raymond K. (Pittsford,
NY), Grammatica; Steven J. (Penfield, NY) |
Assignee: |
Xerox Corporation (Stamford,
CT)
|
Family
ID: |
25222121 |
Appl.
No.: |
07/816,994 |
Filed: |
January 3, 1992 |
Current U.S.
Class: |
430/64;
430/59.6 |
Current CPC
Class: |
G03G
5/142 (20130101) |
Current International
Class: |
G03G
5/14 (20060101); G03G 005/14 () |
Field of
Search: |
;430/64,62,63,58 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Goodrow; John
Claims
What is claimed is:
1. An electrophotographic imaging member comprising a supporting
substrate, a charge blocking layer, an imaging layer comprising at
least one photoconductive layer, said blocking layer comprising an
uncrosslinked chemically modified copolymer derived from vinyl
hydroxy ester or vinyl hydroxy amide repeat units, between about 21
and about 75 mole percent of said vinyl hydroxy ester or vinyl
hydroxy amide repeat units being chemically modified at a
nucleophilic hydroxyl group by a monofunctional electrophile, said
copolymer having a number average molecular weight of at least
about 10,000.
2. An electrophotographic imaging member according to claim 1
wherein said vinyl hydroxy ester or vinyl hydroxy amide repeat
units make up between about 50 and about 100 mole percent of said
polymer prior to chemical modification.
3. An electrophotographic imaging member according to claim 1
wherein an average of between about 30 mole percent and about 50
mole percent of said vinyl hydroxy ester or vinyl hydroxy amide
repeat units is chemically modified by said monofunctional
electrophile.
4. An electrophotographic imaging member according to claim 1
wherein between about 40 and about 60 mole percent of said vinyl
hydroxy ester or vinyl hydroxy amide repeat units is chemically
modified by said monofunctional electrophile.
5. An electrophotographic imaging member according to claim 1
wherein said polymer is a copolymer comprising at least about 50
mole percent of said vinyl hydroxy ester or vinyl hydroxy amide
repeat units prior to chemical modification.
6. An electrophotographic imaging member according to claim 1
wherein said copolymer is a terpolymer comprising at least about 50
mole percent of said vinyl hydroxy ester or vinyl hydroxy amide
repeat units prior to chemical modification.
7. An electrophotographic imaging member according to claim 1
wherein said vinyl hydroxy ester or vinyl hydroxy amide repeat
units are chemically modified prior to the formation of said
copolymer.
8. An electrophotographic imaging member according to claim 1
wherein said vinyl hydroxy ester or vinyl hydroxy amide repeat
units are chemically modified after formation of said
copolymer.
9. An electrophotographic imaging member according to claim 1
wherein said imaging layer comprises a charge generating layer and
a charge transport layer.
10. An electrophotographic imaging member according to claim 1
wherein said monofunctional electrophile is selected from the group
consisting of a carboxylic acid chloride, a carboxylic acid
anhydride and an isocyanate, a sulfonyl chloride, an alkyl halide,
an activated aryl halide, an activated ester, and reactive
monofunctional heteroatom halides.
11. An electrophotographic imaging member according to claim 1
wherein said blocking layer comprises a blend of said chemically
modified vinyl hydroxy ester or vinyl hydroxy amide copolymer and a
completely chemically modified vinyl hydroxy ester or vinyl hydroxy
amide polymer.
12. An electrophotographic imaging member according to claim 1
wherein said blocking layer comprises a blend of said chemically
modified vinyl hydroxy ester or vinyl hydroxy amide copolymer, an
unmodified vinyl hydroxy ester or vinyl hydroxy amide polymer, and
a completely chemically modified vinyl hydroxy ester or vinyl
hydroxy amide polymer.
13. An electrophotographic imaging member according to claim 1
wherein said blocking layer comprises a blend of said chemically
modified vinyl hydroxy ester or vinyl hydroxy amide copolymer and
an unmodified vinyl hydroxy ester or vinyl hydroxy amide
polymer.
14. An electrophotographic imaging member according to claim 13
wherein said blocking layer comprises between about 50 mole percent
and about 99.5 mole percent of said unmodified vinyl hydroxy ester
or vinyl hydroxy amide polymer, based on the total repeat units in
said blocking layer.
15. An electrophotographic imaging member according to claim 13
wherein said unmodified vinyl hydroxy ester or vinyl hydroxy amide
polymer comprises vinyl hydroxy ester or vinyl hydroxy amide repeat
units represented by the following formula: ##STR10## wherein: R',
R" and R'" are independently selected from the group consisting of
hydrogen, aliphatic, aromatic, heteroaliphatic, heteroaromatic,
fused aromatic ring and heteroaromatic ring groups containing up to
10 carbon atoms,
x represents the number of unmodified repeat units in the
homopolymer,
X is selected from the group consisting of groups represented by
the following groups: ##STR11## wherein R is selected from the
group consisting of aliphatic, aromatic, heteroaliphatic,
heteroaromatic, fused aromatic ring and heteroaromatic ring groups
containing up to 10 carbon atoms, and
z is from 1 to 10 hydroxyl groups.
16. An electrophotographic imaging member according to claim 1
wherein said vinyl hydroxy ester or vinyl hydroxy amide repeat
units in said chemically modified copolymer are represented by the
following formula: ##STR12## wherein for Unmodified Repeat Unit A:
R', R" and R'" are independently selected from the group consisting
of hydrogen, aliphatic, aromatic, heteroaliphatic, heteroaromatic,
fused aromatic ring and heteroaromatic ring groups containing up to
10 carbon atoms,
x represents the number of repeat units of Unmodified Repeat Unit A
in said polymer and which can be 0 or greater,
X is selected from the group consisting of groups represented by
the following: ##STR13## wherein R is selected from the group
consisting of aliphatic, aromatic, heteroaliphatic, heteroaromatic,
fused aromatic ring and heteroaromatic ring groups containing up to
10 carbon atoms, and
z is from 1 to 10 hydroxyl groups, and
wherein for Modified Repeat Unit B:
R', R" and R'" are independently selected from the group consisting
of hydrogen, aliphatic, aromatic, heteroaliphatic, heteroaromatic,
fused aromatic ring and heteroaromatic ring groups containing up to
10 carbon atoms,
y represents the number of repeat units of Modified Repeat Unit B
in the copolymer and x plus y represent sufficient repeat units for
a molecular weight of at least about 10,000,
X' is selected from the group consisting of groups represented by
the following: ##STR14## wherein R is selected from the group
consisting of aliphatic, aromatic, heteroaliphatic, heteroaromatic,
fused aromatic ring and heteroaromatic ring groups containing up to
10 carbon atoms,
Z represents a moiety from the monofunctional electrophile, and
z and z' are whole numbers wherein:
z.gtoreq.z', and
z minus z'=the remaining hydroxyl groups per repeat unit.
17. An electrophotographic imaging member according to claim 1
wherein said imaging member comprises said charge blocking layer, a
charge generating layer, and a thin continuous interfacial zone at
the interface between said charge blocking layer and said charge
generating layer, said charge generating layer comprising a film
forming polymer partially compatible with said chemically modified
copolymer and said interfacial zone comprising a mixture of said
film forming polymer and said chemically modified polymer.
18. An electrophotographic imaging process comprising an
electrophotographic imaging member comprising a supporting
substrate, a charge blocking layer, an imaging layer comprises at
least one photoconductive layer, said blocking layer comprising an
uncrosslinked copolymer derived from vinyl hydroxy ester or vinyl
hydroxy amide repeat units, between about 21 and about 75 mole
percent of said vinyl hydroxy ester or vinyl hydroxy amide repeat
units being chemically modified at a nucleophilic hydroxyl group by
a monofunctional electrophile, said polymer having a number average
molecular weight of at least about 10,000, forming an electrostatic
latent image on said imaging surface, contacting said imaging
surface with a developer comprising electrostatically attractable
marking particles whereby said electrostatically attractable
marking particles deposit on said imaging surface in conformance
with said electrostatic latent image to form a marking particle
image, transferring said marking particle image to a receiving
member, and repeating said forming, contacting and transferring
steps at least once.
19. An electrophotographic imaging process according to claim 18
wherein said blocking layer also comprises an unmodified vinyl
hydroxy ester or vinyl hydroxy amide polymer.
20. An electrophotographic imaging process according to claim 18
wherein said vinyl hydroxy ester or vinyl hydroxy amide repeat
units are represented by the following formula: ##STR15## wherein
for Unmodified Repeat Unit A: R', R" and R'" are independently
selected from the group consisting of hydrogen, aliphatic,
aromatic, heteroaliphatic, heteroaromatic, fused aromatic ring and
heteroaromatic ring groups containing up to 10 carbon atoms,
x represents the number of repeat units of Unmodified Repeat Unit A
in said polymer and which can be 0 or greater,
X is selected from the group consisting of groups represented by
the following: ##STR16## wherein R is selected from the group
consisting of aliphatic, aromatic, heteroaliphatic, heteroaromatic,
fused aromatic ring and heteroaromatic ring groups containing up to
10 carbon atoms, and
z is from 1 to 10 hydroxyl groups, and
wherein for Modified Repeat Unit B:
R', R" and R'" are independently selected from the group consisting
of hydrogen, aliphatic, aromatic, heteroaliphatic, heteroaromatic,
fused aromatic ring and heteroaromatic ring groups containing up to
10 carbon atoms,
y represents the number of repeat units of Modified Repeat Unit B
in the copolymer and x plus y represent sufficient repeat units for
a molecular weight of at least about 10,000,
X' is selected from the group consisting of groups represented by
the following: ##STR17## wherein R is selected from the group
consisting of aliphatic, aromatic, heteroaliphatic, heteroaromatic,
fused aromatic ring and heteroaromatic ring groups containing up to
10 carbon atoms,
Z represents a moiety from the monofunctional electrophile, and z
and z' are whole numbers wherein:
z.gtoreq.z', and
z minus z'=the remaining hydroxyl groups per repeat unit.
Description
BACKGROUND OF THE INVENTION
This invention relates in general to electrophotography and, more
specifically, to a novel photoconductive device and process for
using the device.
A photoconductive layer for use in electrophotography may be a
homogeneous layer of a single material such as vitreous selenium or
it may be a composite layer containing a photoconductor and another
material. One type of composite photoconductive layer used in
electrophotography is illustrated in U.S. Pat. No. 4,265,990 which
describes a photosensitive member having at least two electrically
operative layers. One layer comprises a photoconductive layer which
is capable of photogenerating holes and injecting the
photogenerated holes into a contiguous charge transport layer.
Various combinations of materials for charge generating layers
(CGL) and charge transport layers (CTL) have been investigated. For
example, the photosensitive member described in U.S. Pat. No.
4,265,990 utilizes a charge generating layer in contiguous contact
with a charge transport layer comprising a polycarbonate resin and
one or more of certain diamine compounds. Various generating layers
comprising photoconductive layers exhibiting the capability of
photogeneration of holes and injection of the holes into a charge
transport layer have also been investigated. The charge generation
layer may comprise a homogeneous photoconductive material or
particulate photoconductive material dispersed in a binder. Other
examples of homogeneous and binder charge generation layer are
disclosed, for example, in U.S. Pat. No. 4,265,990. Additional
examples of binder materials such as poly(hydroxyether) resins are
taught in U.S. Pat. No. 4,439,507. The disclosures of the aforesaid
U.S. Pat. No. 4,265,990 and U.S. Pat. No. 4,439,507 are
incorporated herein in their entirety. Photosensitive members
having at least two electrically operative layers as disclosed
above provide excellent images when charged with a uniform negative
electrostatic charge, exposed to a light image and thereafter
developed with finely divided electroscopic marking particles.
Where polymers such as vinyl hydroxy ester or vinyl hydroxy amide
polymers are utilized in adjacent charge blocking layers, poor
adhesion is encountered and an additional intervening adhesive is
often desirable. Also, when some binder materials are employed in a
blocking layer or charge generating layer, the binder can be
attacked by some of the solvents employed to apply subsequent
layers. Solvent attack of an underlying layer such as the blocking
layer cannot normally be tolerated in precision copiers,
duplicators, and printers.
INFORMATION DISCLOSURE STATEMENT
EP 0 448 780 A1 to Spiewak et al, published Oct. 10, 1991--An
electrophotographic imaging member is disclosed containing a
substrate having an electrically conductive surface, a charge
blocking layer including a vinyl hydroxy ester or vinyl hydroxy
amide polymer and at least one photoconductive layer. The vinyl
hydroxy ester or vinyl hydroxy amide polymer may be reacted with
polyfunctional compounds to crosslink the polymer.
U.S. Pat. No. 4,535,045 issued to Kawamura et al on Aug. 13,
1985--appears to disclose a light-sensitive layer comprising a
vinylidene chloride or vinyl chloride, a vinyl based unsaturated
monomer, and a vinyl monomer comprising a hydroxyl group. The vinyl
monomer may comprise hydroxyethyl acrylate, hydroxyethyl
methacrylate, and 2-hydroxypropyl methacrylate (e.g. see column 4,
line 60-column 5, line 15).
U.S. Pat. No. 3,595,647 issued to Yasumori et al on Jul. 27,
1971--A photoconductive layer is disclosed comprising a binder
comprising a mixture composed of (1) a copolymer of hydroxyethyl-
(or meth-) acrylate and vinyl monomer having carboxylic acid
radicals; (2) a mixture of a copolymer formed from carboxylic acid
monomer, vinyl monomer, and an organic acid anhydride; and (3) a
mixture comprising the copolymer in (1) and the organic acid
anhydride of (2).
U.S. Pat. No. 3,554,747 issued to Dastoor on Jan. 12, 1971--An
electrostatic printing material is disclosed comprising a
conductive support layer and a second layer wherein the second
layer comprises a polymeric binder. The polymeric binder comprises
ethyl acrylate selected from the group comprising hydroxyethyl
methacrylate and hydroxypropyl methacrylate (e.g. see column 2,
lines 27-52).
U.S. Pat. No. 3,672,889 issued to Baltazzi et al on Jun. 27,
1972--A polymeric resin binder is disclosed comprising a terpolymer
comprising ethyl acrylate or ethyl methacrylate, a vinyl-aryl
compound such as styrene, and an acrylate composed of amino,
hydroxy, or acid functional groups (e.g. see column 2, lines
38-72).
Thus, the characteristics of photosensitive members comprising a
support having a conductive layer, a charge blocking layer and at
least one photoconductive layer, exhibit deficiencies as
electrophotographic imaging members.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an electrophotographic
imaging member which overcomes the above-noted disadvantages.
It is another object of this invention to provide an
electrostatographic imaging member having extended life.
It is another object of this invention to provide an
electrostatographic imaging member exhibiting improved adhesion
between layers, particularly between a charge blocking layer and a
charge generating layer.
It is another object of this invention to provide an
electrostatographic imaging member that charges to high voltages
useful in xerography.
It is another object of this invention to provide an
electrostatographic imaging member which allows photodischarge with
low dark decay and low residual voltage during extended
cycling.
It is another object of the invention to provide an
electrostatographic imaging member that is simpler to
fabricate.
It is another object of the invention to provide an
electrostatographic imaging member having a blocking layer that is
resistant to disturbance or dissolving by components of
subsequently applied layers.
These and other objects of the present invention are accomplished
by providing an electrophotographic imaging member comprising a
supporting substrate, an imaging layer comprising at least one
photoconductive layer, the blocking layer comprising an
uncrosslinked copolymer derived from vinyl hydroxy ester or vinyl
hydroxy amide repeat units some of which have been chemically
modified at the nucleophilic hydroxyl group by a monofunctional
electrophile, the copolymer having a number average molecular
weight of at least about 10,000. This imaging member may be
employed in an electrostatographic imaging process.
The supporting substrate layer having an electrically conductive
surface may comprise any suitable rigid or flexible member such as
a flexible web or sheet. The supporting substrate layer having an
electrically conductive surface, may be opaque or substantially
transparent, and may comprise numerous suitable materials having
the required mechanical properties. For example, it may comprise an
underlying insulating support layer coated with a thin flexible
electrically conductive layer, or merely a conductive layer having
sufficient internal strength to support the electrophotoconductive
layer. Thus, the electrically conductive layer may comprise the
entire supporting substrate layer or merely be present as a
component of the supporting substrate layer, for example, as a thin
flexible coating on an underlying flexible support member.
The electrically conductive layer may comprise any suitable
electrically conductive organic or inorganic material. Typical
electrically conductive layers including, for example, aluminum,
titanium, nickel, chromium, brass, gold, stainless steel, carbon
black, graphite, metalloids, cuprous iodide, indium tin oxide
alloys, Lewis acid doped polypyrrole and the like. The electrically
conductive layer may be homogeneous or heterogeneous, e.g.
conductive particles dispersed in a film forming binder. When hole
injecting materials such as carbon black, copper iodide, gold and
other noble metals, platinum, polypyrrole, polyaromatic conducting
polymers, polythiophenes, conducting metallic oxide such as
antimony tin oxide, indium tin oxide, and the like are utilized in
a conductive layer, photoreceptors that do not contain a suitable
blocking layer can often discharge in the dark thereby rendering
the photoreceptor unsuitable for electrophotographic imaging. The
ground plane should be continuous and at least monomolecular in
thickness. The continuous conductive layer may vary in thickness
over substantially wide ranges depending on the desired use of the
electrophotoconductive member. Accordingly, the conductive layer
can generally range, for example, in thicknesses of from about 50
Angstrom units for some materials to many centimeters. For some
ground planes, such as those containing carbon black, a minimum
thickness of about 0.5 micrometer is preferred. When a highly
flexible photoresponsive imaging device is desired, the thickness
of conductive layers may be between about 100 Angstroms to about
2,000 Angstroms. The resistivity of the ground plane should be less
than about 10.sup.8 and more preferably 10.sup.6 ohms/square for
efficient photoreceptor discharge during repeated cycling. If an
underlying flexible support layer is employed, it may be of any
conventional material including metal, plastics and the like.
Typical underlying flexible support layers include insulating or
non-conducting materials comprising various resins or mixtures
thereof with conductive particles, such as metals, carbon black and
the like, known for this purpose including, for example,
polyesters, polycarbonates, polyamides, polyurethanes, and the
like. The coated or uncoated supporting substrate layer having an
electrically conductive surface may be rigid or flexible and may
have any number of different configurations such as, for example, a
sheet, a cylinder, a scroll, an endless flexible belt, and the
like. Preferably, the flexible supporting substrate layer having an
electrically conductive surface comprises an endless flexible belt
of commercially available polyethylene terephthalate polyester
coated with a thin flexible metal coating. Generally, the material
selected for the ground plane should not be attacked by solvents
ultimately selected for use with the subsequently applied blocking
layer. If the blocking layer solvent attacks the ground plane, it
may leach out and/or physically dislodge hole injecting components
from the ground plane into the blocking layer. In subsequent
coating operations, these already migrated hole injection
components in the blocking layer may further migrate into the
charge generating layer or charge transporting layer from which
dark discharge and low charge acceptance can occur. Since hole
injection in the charge generating layer or charge transporting
layer is cumulative with xerographic cycling, V.sub.0 also
decreases with cycling (V.sub.0 cycle-down).
A charge blocking layer is interposed between the conductive
surface and the imaging layer. The imaging layer comprises at least
one photoconductive layer. This blocking layer material traps
positive charges. The charge blocking layer of this invention
comprises a uniform, continuous, coherent blocking layer comprising
an uncrosslinked polymer derived from vinyl hydroxy ester or vinyl
hydroxy amide repeat units chemically modified at least in part at
the nucleophilic hydroxyl group by a monofunctional electrophile.
The improved adhesion achieved by the use of the blocking layer of
this invention eliminates the need for an adhesive layer between
the blocking layer and the adjacent photoconductive layer while
simultaneously maintaining acceptable, stable cyclic electrical
properties. Depending upon the specific composition of the
photoconductive layer utilized, improvements in adhesion using only
the blocking layer of this invention instead of the combination of
a siloxane blocking layer and a polyester adhesive layer ranged
from a 100 percent improvement to an improvement of over 3,900
percent. This improvement in adhesion is especially desirable for
preventing delamination of flexible, welded or seamless
photoreceptor belts.
The chemically modified copolymer of the blocking layer of this
invention is preferably derived from vinyl hydroxy ester or vinyl
hydroxy amide repeat units some of which have been chemically
modified at the nucleophilic hydroxyl group by a monofunctional
electrophile. Chemical modification of the vinyl hydroxy ester or
vinyl hydroxy amide repeat units at the nucleophilic hydroxyl group
by a monofunctional electrophile may be effected on these polymeric
repeat units after polymerization or the same chemical modification
may be effected on the vinyl hydroxy ester or vinyl hydroxy amide
monomers prior to polymerization. Preferably, the vinyl hydroxy
ester or vinyl hydroxy amide repeat units make up between about 50
mole percent and about 100 mole percent of the copolymer prior to
chemical modification.
A chemically modified polymer may be a homopolymer if 100 percent
modified by the same modifier or may be a copolymer if not
completely modified or if the unmodified polymer was modified by
more than one modifier, but the partially modified copolymer will
always be a component of the blocking layer composition of this
invention whereas the 100 percent chemically modified homopolymer
or 100 percent unmodified homopolymer may not always be a blocking
layer component of this invention. However in some preferred
adhesive blocking layer embodiments of this invention, the
unmodified vinyl hydroxy ester or vinyl hydroxy amide homopolymer
having the same unmodified repeat unit that resides in the modified
copolymer to be mixed with the homopolymer (every vinyl hydroxy
ester or vinyl hydroxy amide modified copolymer must have some
unmodified repeat units) produces blocking layer blends with
excellent interfacial adhesion between the charge generating layer
and the blocking layer. The modified vinyl hydroxy ester or vinyl
hydroxy amide copolymer may be a random copolymer of 2 or more
different monomers or a block or segmented (segmented means a short
block that occurs more frequently than the longer block) copolymer
of 2 or more different monomers. The random copolymers are
preferred because of their relative ease of synthesis or
availability. Moreover, the modified vinyl hydroxy ester or vinyl
hydroxy amide copolymers in this invention can contain a random or
non-blocky or non-segmented repeat unit sequence in which are
contained atactic, syndiotactic and/or isotactic triad sequences.
Optionally the copolymers can contain a blocked or segmented repeat
unit sequence in which are contained atactic, syndiotactic, and/or
isotactic triad sequences. All possible copolymer repeat unit
sequences and tacticity sequences may co-exist in the modified and
unmodified copolymers of this invention. If desired, the blocking
layer may comprise a blend of one or more chemically modified
copolymers, or may comprise a blend of one or more chemically
modified copolymers blended with either or both--one or more
chemically unmodified homopolymers or--one or more 100 percent
chemically modified homopolymers.
The uncrosslinked vinyl hydroxy ester or vinyl hydroxy amide
polymer, prior to chemical modification of vinyl hydroxy ester or
vinyl hydroxy amide repeat units at the nucleophilic hydroxyl group
by a monofunctional electrophile, may be a homopolymer or a
copolymer. Preferred vinyl hydroxy ester or vinyl hydroxy amide
repeat units prior to chemical modification are represented by the
following formula: ##STR1## wherein: x represents sufficient repeat
units for a total polymer molecular weight of at least about
10,000,
X is selected from the group consisting of groups represented by
the following groups:
R is selected from the group consisting of aliphatic, aromatic,
heteroaliphatic, heteroaromatic, fused aromatic ring and
heteroaromatic ring groups containing up to 10 carbon atoms;
z contains from 1 to 10 hydroxyl groups; and ##STR2## R', R" and
R'" are independently selected from the group consisting of
hydrogen, aliphatic, aromatic, heteroaliphatic, heteroaromatic,
fused aromatic ring and heteroaromatic ring groups containing up to
10 carbon atoms.
Typical divalent R aliphatic groups include methylene, ethylene,
propylene, ethylidene, propylidene, isopropylidene, butylene,
isobutylene, decamethylene, phenylene, biphenylene, piperadinylene,
tetrahydrofuranylene, pyranylene, piperazinylene, pyridylene,
bipyridylene, pyridazinylene, pyrimidinylene, naphthylidene,
quinolinyldene, cyclohexylene, cyclopentylene, cyclobutylene,
cycloheptylene, and the like.
Typical monovalent R', R" and R'" groups include hydrogen, methyl,
ethyl, propyl, isopropyl, butyl, isobutyl, decyl, phenyl, biphenyl,
piperadinyl, tetrahydrofuranyl, pyranyl, piperazinyl, pyridyl,
bipyridyl, pyridazinyl, naphthyl, quinolinyl, cyclohexyl,
cyclopentyl, cyclobutyl, cycloheptyl, and the like. Preferably, R'
and R" are hydrogen.
Typical aliphatic, aromatic, heteroaliphatic, heteroaromatic, fused
aromatic ring and heteroaromatic ring groups containing up to 10
carbon atoms include linear, single ring and multiple ring, fused
and unfused groups such as naphthalene, thiophene, quinoline,
pyridine, furan, pyrrole, isoquinoline, benzene, pyrazine,
pyrimidine, bipyridine, pyridazine, and the like.
The uncrosslinked polymers described above involving at least a
vinyl hydroxy ester or vinyl hydroxy amide monomer that contain
vinyl hydroxy ester or vinyl hydroxy amide repeat units that have
not been chemically modified through a nucleophilic hydroxyl group
by a monofunctional electrophile are described in copending U.S.
patent application Ser. No. 07/691,180 filed on Apr. 25, 1991 to
Spiewak et al, which is a continuation application of U.S. patent
application Ser. No. 07/459,916 filed on Dec. 29, 1989. The
European patent application corresponding to U.S. patent
application Ser. No. 07/459,916 is EP 0 448 780 A1 published Oct.
10, 1991. The entire disclosures of U.S. patent application Ser.
No. 07/691,180 filed on Apr. 25, 1991 and EP 0 448 780 A1 published
Oct. 10, 1991 are incorporated herein by reference.
Typical chemically unmodified vinyl hydroxy ester polymers and
vinyl hydroxy amide polymers include the following unmodified
homopolymers and any copolymer combinations thereof:
poly(2-hydroxyethyl)methacrylate, poly(2-hydroxyethyl)acrylate,
poly(2-hydroxypropyl)methacrylate, poly(2-hydroxypropyl)acrylate,
poly(4-hydroxybutyl)methacrylate, poly(4-hydroxybutyl)acrylate,
poly(3-hydroxypropyl)methacrylate, poly(3-hydroxypropyl)acrylate,
poly(2,3-dihydroxypropyl)methacrylate,
poly(2,3-dihydroxypropyl)acrylate,
poly(2,3,4-trihydroxybutyl)methacrylate,
poly(2,3,4-trihydroxybutyl)acryla te, poly(N-2,3
dihydroxypropyl)methacrylamide, poly(N-2,3
dihydroxypropyl)acrylamide, poly(N-hydroxymethyl)methacrylamide,
poly(N-hydroxymethyl)acrylamide,
poly(N-2-hydroxyethyl)methacrylamide,
poly(N-2-hydroxyethyl)acrylamide,
poly(4-hydroxyphenyl)methacrylate, poly(4-hydroxyphenyl)acrylate,
poly(3-hydroxyphenyl)methacrylate, poly(3-hydroxyphenyl)acrylate,
poly(N-3 or 4-hydroxyphenyl)methacrylamide, poly(N-3 or
4-hydroxyphenyl)acrylamide, poly[4(2-hydroxypyridyl]methacrylate,
poly[4(2-hydroxypyridyl]acrylate,
poly[4(3-hydroxypiperidinyl]methacrylate,
poly[4(3-hydroxypiperidinyl]acrylate,
poly[N-4(2-hydroxypyridyl]methacrylamide,
poly[N-4(2-hydroxypyridyl]acrylamide,
poly[N-4(3-hydroxypiperindinyl]methacrylamide,
poly[N-4(3-hydroxypiperindinyl]acrylamide,
poly[1(5-hydroxynaphthyl]methacrylate,
poly[1(5-hydroxynaphthyl]acrylate,
poly[N-1(5-hydroxyethylnaphthyl]methacrylamide,
poly[N-1(5-hydroxyethylnaphthyl]acrylamide,
poly[1(4-hydroxycyclohexyl]methacrylate,
poly[1(4-hydroxycyclohexyl]acrylate,
poly[N-1(3-hydroxycyclohexyl]methacrylamide,
poly[N-1(3-hydroxycyclohexyl]acrylamide, and the like.
Modified Copolymers and Blends of Modified Copolymers
Typical preferred uncrosslinked vinyl hydroxy ester or vinyl
hydroxy amide copolymers containing both chemically modified vinyl
hydroxy ester or vinyl hydroxy amide repeat units (repeat unit B)
and unmodified vinyl hydroxy ester or amide repeat units (repeat
unit A) wherein the chemical modification was carried out at the
nucleophilic hydroxyl group by a monofunctional electrophile may be
represented by the following formula: ##STR3## wherein for
Unmodified Repeat Unit A: R', R" and R'" are independently selected
from the group consisting of hydrogen, aliphatic, aromatic,
heteroaliphatic, heteroaromatic, fused aromatic ring and
heteroaromatic ring groups containing up to 10 carbon atoms,
x represents the number of repeat units of unmodified repeat unit
A,
X is selected from the group consisting of groups represented by
the following groups: ##STR4## wherein R is selected from the group
consisting of aliphatic, aromatic, heteroaliphatic, heteroaromatic,
fused aromatic ring and heteroaromatic ring groups containing up to
10 carbon atoms, and
z is from 1 to 10 hydroxyl groups, and
wherein for Modified Repeat Unit B:
R', R" and R'" are independently selected from the group consisting
of hydrogen, aliphatic, aromatic, heteroaliphatic, heteroaromatic,
fused aromatic ring and heteroaromatic ring groups containing up to
10 carbon atoms,
y represents the number of repeat units of modified repeat unit B
in one or more modified copolymers comprising the blocking layer
composition in which y can be any positive whole number,
x plus y represent sufficient repeat units for a molecular weight
of at least about 10,000,
X' is selected from the group consisting of groups represented by
the following groups:
wherein ##STR5## R is selected from the group consisting of
aliphatic, aromatic, heteroaliphatic, heteroaromatic, fused
aromatic ring and heteroaromatic ring groups containing up to 10
carbon atoms,
Z represents a moiety from the monofunctional electrophile, and
z and z' are whole numbers.
As indicated above, x represents the number of repeat units of
unmodified repeat unit A in the one or more modified copolymer(s)
comprising the blocking layer composition (no homopolymers in this
blocking layer composition since x or y never equals 0; the
homopolymer embodiment will be addressed hereinafter) in which x
can be any positive whole number such that the resulting blocking
layer produces satisfactory adhesion to the charge generating
layer; wherein the unmodified repeat units A in each modified
copolymer are between about 25 percent and about 79 percent of all
the repeat units (x+y) in the modified copolymer or, in at least
one modified copolymer in a blend of modified copolymers,
comprising the blocking layer. Unmodified repeat units A in each
modified copolymer between about 50 percent and about 70 percent of
all the repeat units is preferred with optimum results being
achieved with between about 40 percent and about 60 percent.
As specified above, y represents the number of repeat units of
modified repeat unit B in one or more modified copolymers
comprising the blocking layer composition (no homopolymers in this
blocking layer composition since x or y never equals 0) in which y
can be any positive whole number such that the resulting blocking
layer produces satisfactory adhesion to the charge generating
layer; wherein the modified repeat units B in each copolymer are
between about 21 percent and about 75 percent of all the repeat
units (x+y) in the modified copolymer or, in at least one modified
copolymer of a blend of modified copolymers, comprising the
blocking layer. The tabular results in the working Examples suggest
that blocking layers containing modified copolymers having 20 or
less mole percent modified repeat units afford unsatisfactory
adhesion to the charge generating layer. The above range defines
the repeat unit content of the modified copolymers (which are
mandatory components of the blocking layer) for good adhesion. It
is believed that blocking layers containing modified copolymers
having modified repeat unit contents between about 21 mole percent
and about 75 mole percent produce satisfactory adhesion to the
charge generating layer. When the modified content exceeds about 75
mole percent modified repeat units, the solubility of these
blocking layers in subsequently used organic coating solvents
increases to such an extent that significantly poorer electrical
properties due to layer mixing will be encountered.
As to z and z' denoted above, they are whole numbers for modified
copolymers or blends of modified copolymers generated by modifying
one or more vinyl hydroxy ester or vinyl hydroxy amide homopolymer
or copolymer to give sufficient modified repeat units B to meet the
between about 21 mole percent and about 75 mole percent limits and
sufficient unmodified repeat units A to meet the between about 79
mole percent and about 25 mole percent range in at least one of the
modified copolymers of a blend thereof; wherein z in unmodified
repeat units A can be 1-10 and z' in modified repeat units B can
also be 1-10; when z=z,' all the hydroxyl groups in unmodified
repeat unit A have undergone modification to give modified repeat
unit B; and when z' is<z, less than all the hydroxyl groups in
unmodified repeat unit A have undergone modification to give
modified repeat unit B. If modified repeat units are instead
generated at the monomer stage by modifying different vinyl hydroxy
ester or vinyl hydroxy amide monomers containing different amounts
of hydroxy groups per repeat unit, followed by polymerization
thereof, then z and z' become mathematically unrelated to each
other.
The upper molecular weight limit of the chemically modified vinyl
hydroxy ester or vinyl hydroxy amide copolymers, which must at
least in part comprise the blocking layer of this invention, is
determined by the increasing viscosity of the copolymer or
copolymer blend coating solution used in the chosen coating
process. At very high copolymer molecular weights and practically
useful concentrations, the coating solution may be too viscous to
form a uniform coherent blocking layer coating. The lower molecular
weight limit of same is determined by the minimum copolymer
molecular weight (about 10,000) at which the resulting coating will
be coherent and of uniform thickness. The electrophotographic
imaging device performance improves as the blocking layer copolymer
molecular weight increases because high molecular weight copolymers
have improved solvent barrier properties making less likely any
disturbance of the blocking layer or the underlying conductive
layer when solvent coating the upper device layers (e.g. the charge
generating layer and the charge transport layer). Thus, layer
mixing and the deleterious electrical properties resulting
therefrom are less likely when high molecular weight blocking layer
copolymers are used. The same molecular weight considerations apply
to blocking layers of this invention comprising one or more
modified or unmodified homopolymers that may be blended with one or
more modified copolymers.
Polymer Blends Between One or More Modified Copolymers and One or
More Modified or Unmodified Homopolymers
Two types of polymer blends are plausible in formulating the
miscible blocking layer compositions of this invention: (1) blends
of two or more different vinyl hydroxy ester or vinyl hydroxy amide
modified copolymers, already discussed above, and (2) blends of one
or more different vinyl hydroxy ester or vinyl hydroxy amide
modified copolymers with either the same or one or more different
vinyl hydroxy ester or vinyl hydroxy amide homopolymers. The
expression "same" means that the homopolymer repeat units are the
same as those of one of the modified or unmodified repeat units in
one of the modified copolymers used in the blocking layer
composition. Blends between two homopolymers (both modified, or
both unmodified, or one modified and one not modified) are not
considered as blocking layer compositions of this invention because
these blends will not be miscible or will not have improved
adhesive properties or improved solvent resistance to subsequently
used coating solvents.
The chemically modified vinyl hydroxy ester or vinyl hydroxy amide
copolymers may be used alone in the blocking layer of this
invention or blended with other miscible homopolymers or
copolymers. Miscibility is defined as a non-hazy coating (after
drying) of equal amounts of the polymers cast from a common
solution of the two polymers in one solvent. When a blend of two or
more chemically modified vinyl hydroxy ester or vinyl hydroxy amide
copolymers are used alone as the blocking layer composition in this
invention, the copolymers may contain a common unmodified repeat
unit (A) or a common modified repeat unit (B) or may contain no
common repeat units of any kind as long as the dried blocking layer
is visually miscible. Layer clarity arising from polymer
miscibility in the dried coatings allows for the use of backside
light exposure, in a controllable reproduceable manner, to reach
the charge generator layer through transparent conductive and
blocking layers in electrophotographic devices coated upon
transparent belt substrates. For non-transparent substrates such as
a drum or an opaque belt, the layers beneath the charge generator
layer need not be transparent because frontside exposure through
the transparent charge transport layer would be routinely used. In
frontside exposure devices, the adhesive-blocking layers of this
invention may be used in many more combinations without regard for
blocking layer clarity. In such electrically satisfactory blocking
layers, it is the enhanced adhesion to the charge generator layer
(attributable to at least a minimal presence of one or more
modified vinyl hydroxy ester or vinyl hydroxy amide copolymers and
the optional presence of one or more modified or unmodified
homopolymers) that is gained by using the blocking layer polymer
compositions of this invention versus similar blocking layers not
containing a modified vinyl hydroxy ester or vinyl hydroxy amide
component. One or more copolymers represented by the foregoing
formula containing the modified repeat unit B can be blended with
one or more other suitable uncrosslinked homopolymers or copolymers
that contains unmodified or modified repeat units.
Typical preferred unmodified uncrosslinked vinyl hydroxy ester or
vinyl hydroxy amide homopolymers or copolymers that may be blended
with modified copolymers containing the above described modified
Repeat Unit B may be represented by the following formula: ##STR6##
wherein for Unmodified Repeat Unit C: R', R" and R'" are
independently selected from the group consisting of hydrogen,
aliphatic, aromatic, heteroaliphatic, heteroaromatic, fused
aromatic ring and heteroaromatic ring groups containing up to 10
carbon atoms,
x' represents the number of repeat units of uncrosslinked
unmodified repeat unit C in the unmodified copolymer or
homopolymer,
X is selected from the group consisting of groups represented by
the following groups: ##STR7## wherein R is selected from the group
consisting of aliphatic, aromatic, heteroaliphatic, heteroaromatic,
fused aromatic ring and heteroaromatic ring groups containing up to
10 carbon atoms, and
z is from 1 to 10 hydroxyl groups.
As indicated above, x' represents the number of repeat units of
uncrosslinked unmodified repeat unit C in the unmodified copolymer
of homopolymer, used to blend with the essential modified copolymer
of this invention, such that the sum of x' times the repeat unit
molecular weight (for every unmodified repeat unit and its x' in
the unmodified copolymer or homopolymer) equals a minimum of 10,000
molecular weight units for the unmodified homopolymer or copolymer,
and has a maximum molecular weight which is determined when the
coating solution viscosity is too high for effective processing
into a uniform coherent blocking layer coating. The mole percent of
x' unmodified vinyl hydroxy ester or vinyl hydroxy amide repeat
units from all sources (the unmodified repeat units in the
essential modified copolymer and the unmodified repeat units in the
optional unmodified homopolymer or copolymer) in a satisfactory
transparent blocking layer composition (one polymer component or a
blend of polymers) of this invention can be very large while still
obtaining at least satisfactory adhesion at the charge generator
layer-blocking layer interface. For example, Device 2 in Table IA
in Example II has excellent adhesion when 97.5 mole percent of the
blocking layer composition is comprised of unmodified repeat units;
that is only 2.5 mole percent of all the repeat units in the
blocking layer composition are modified. Preferably the blocking
layer of this invention contains at least about 0.5 mole percent
modified repeat unit from the essential, one or more, modified
copolymer sources and up to about 99.5 mole percent of unmodified
repeat unit from the optional, one or more, unmodified homopolymer
or copolymer sources for securing high adhesion of at least 10
grams/cm in adhesion peel tests at the charge generator-blocking
layer interface.
The upper (mole percent modified repeat unit content) end of the
preferred range is as previously defined for a modified copolymer
or blend of modified copolymers. Thus, for a blocking layer
composition containing one or more modified vinyl hydroxy ester or
vinyl hydroxy amide copolymers blended with one or more unmodified
vinyl hydroxy ester or vinyl hydroxy amide copolymers or
homopolymers, the upper modified repeat unit content limit will
again be defined as that amount, which when exceeded, causes the
device electrical properties to deteriorate to an unsatisfactory
level for the intended machine application due to interlayer mixing
caused by too much modified copolymer in the blocking layer
composition. A suitable numerical value previously given to this
preferred upper limit of modified vinyl hydroxy ester or vinyl
hydroxy amide repeat units in a modified copolymer is 75 mole
percent (in any given copolymer not in the entire blocking layer
composition), when only a modified copolymer or a blend of modified
copolymer were used as the entire blocking layer composition. With
one or more optional unmodified homopolymers or copolymers also
blended into the blocking layer composition with the one or more
essential modified vinyl hydroxy ester or vinyl hydroxy amide
copolymers, the total number of modified repeat units is preferably
between about 0.5 mole percent about 50 mole percent and the total
number of unmodified repeat units is preferably between about 50
mole percent and about 99.5 mole percent. It is imperative,
however, that at least one of the essential one or more modified
copolymers, used with one or more optional unmodified homopolymers
or copolymers also blended into the blocking layer composition with
the one or more essential modified vinyl hydroxy ester or vinyl
hydroxy amide copolymers, or in any other blended or non-blended
blocking layer compositions described in this invention, have a
minimum of 21 mole percent modified repeat units up to a maximum of
about 75 mole percent modified repeat units in the modified
copolymer in order to achieve the preferred level of adhesion
improvement, that is to at least 10 grams/cm peel strength.
The vinyl hydroxy ester or vinyl hydroxy amide polymer containing
unmodified repeat unit C may be a homopolymer or a copolymer
wherein the copolymer is defined as any polymer having 2 or more
different repeat units which also includes terpolymers. Such
polymers containing unmodified repeat unit C, if present as part of
a blend with the chemically modified copolymer, are often a
homopolymer of 100 percent unmodified repeat unit A. Such polymers
containing unmodified repeat unit C may be unique and have a
composition different from that of Repeat Unit A in which one or
more of R', R", R'" and X or X' will be different from the R', R",
R'" and X in repeat unit A. The unmodified repeat unit C, if part
of an unmodified copolymer containing vinyl hydroxy ester and/or
vinyl hydroxy amide repeat units, may also comprise non vinyl
hydroxy ester and/or amide repeat units.
Generally, if non-vinyl hydroxy ester and/or non-vinyl hydroxy
amide repeat units are included in the blocking layer composition,
these repeat units and the unmodified vinyl hydroxy ester and/or
vinyl hydroxy amide repeat units, that must be included, should be
copolymerized together from their respective monomers. However, if
non-vinyl hydroxy ester and/or non-vinyl hydroxy amide repeat units
are included with modified vinyl hydroxy ester and/or vinyl hydroxy
amide repeat units in the same copolymer of the blocking layer
composition, then the copolymer can either be formed from monomers
or can be formed by chemical modification of the nucleophilic
hydroxyl groups ( in the corresponding unmodified vinyl hydroxy
ester and/or vinyl hydroxy amide repeat units) by an appropriate
electrophile. A variety of vinyl monomers can be copolymerized with
either the unmodified or modified vinyl hydroxy ester and/or vinyl
hydroxy amide monomers. These include styrene and its derivatives,
vinyl acetate, acrylonitrile and methacrylonitrile,
N-vinylpyrrolidone, all the acrylics including methyl, ethyl,
propyl, butyl and 2-ethylhexyl acrylates and methacrylates, acrylic
and methacrylic acid, acrylamide and methacrylamide and all their
derivatives including N-methyl, N,N-dimethyl and the
N-isobutoxymethyl derivative and the like. Additional conjugated
monomers include butadiene, isoprene, chloroprene and the like.
Some fluorine containing monomers that also may be copolymerizable
with either the unmodified or modified vinyl hydroxy ester and/or
vinyl hydroxy amide monomers include tetrafluoroethylene,
vinylidene fluoride, vinyl fluoride, and
2-(N-ethylperfluorooctanesulfonamide) ethyl acrylate or
methacrylate and the like. The number (mole percent) of non-vinyl
hydroxy ester and/or non-vinyl hydroxy amide repeat units in
copolymers also containing modified and/or unmodified vinyl hydroxy
ester and/or vinyl hydroxy amide repeat units will have an upper
limit value that is determined by whether the copolymer is miscible
with the other polymers in the blocking layer composition, which
upper limit value is variable and unpredictable and a function of
the chemical structure of the non-vinyl hydroxy ester and/or
non-vinyl hydroxy amide repeat units in said copolymer. The lower
limit value of the non-vinyl hydroxy ester and/or non-vinyl hydroxy
amide repeat units in the copolymer probably has no significance
and is about 0.5 mole percent. In addition, the copolymer
(described in the preceding sentence) in the blocking layer
composition should provide a satisfactory (at least up to about 5
grams/cm peel strength) improvement in adhesion to the selected
charge generator layer binder material. In addition, many blocking
layer copolymers containing appreciable amounts of non-vinyl
hydroxy ester and/or non-vinyl hydroxy amide repeat units may
become too soluble in subsequently used coating solvents resulting
in interlayer mixing and unacceptable electrical properties; so the
mole percentage of the repeat units must be carefully monitored to
avoid this problem. Occasionally the reverse solubility problem
arises--that is the kind and amount of non-vinyl hydroxy ester
and/or non-vinyl hydroxy amide repeat units in the blocking layer
copolymer needed to obtain transparency and improved adhesion may
cause the copolymer to become too insoluble in commonly used
blocking layer coating solvents, making the blocking layer
composition non-processable and therefore useless. Transparent
blocking layers in belts containing mostly transparent substrates
and conductive layers are a preferred embodiment. Generally, a
transparent or non-transparent blocking layer can be used on drum
electrophotographic devices providing that the blocking layer has
the required electrical, adhesive, and solvent barrier
properties.
Other examples of miscible polymers include polyethyloxazoline
(available from Dow Chemical Company) and any other sufficiently
basic organic polymers capable of forming strong H-bonding
complexes with vinyl hydroxy ester and/or vinyl hydroxy amide
repeat units in the essential modified copolymer blocking layer
component of the blocking layer composition so that visual phase
separation or immiscibility is inhibited. It is believed that these
basic organic polymers would include poly(ethylene and propylene)
imines and other organic nitrogen containing basic polymers and the
like, but not poly(vinylpyridines).
Since quantitative or near quantitative modification of high
molecular weight vinyl hydroxy ester and/or vinyl hydroxy amide
polymers is difficult to achieve, the chemically modified blocking
layer copolymers and homopolymers having between about 75 and about
100 percent modified repeat units are best arrived at by carrying
out the appropriate chemical modification on the vinyl hydroxy
ester and/or amide monomer(s) followed by homopolymerization or
copolymerization thereof. The resulting modified polymer will be a
modified homopolymer if there is only one monomer that is modified
with one modifier; or the resulting modified polymer will be a
modified copolymer if one or more modified monomers, modified with
one or more different modifiers, is copolymerized with one or more
unmodified or modified monomers. Chemically modified copolymers,
having a modification level less than about 75 mole percent of the
vinyl hydroxy ester and/or vinyl hydroxy amide repeat units, are
best arrived at by chemically modifying at the nucleophilic
hydroxyl site with an appropriate modifying electrophile. Since the
highest preferred vinyl hydroxy ester and/or vinyl hydroxy amide
copolymer modification level described in the examples of this
invention was less than about 75 mole percent, the polymer
modification route was employed as a synthetic route to the
copolymers in this invention, but this is not intended to be
limiting in any way which means that the monomer modification route
could optionally have been used.
Other blocking layer composition embodiments of this invention
include:
(1) Those blocking layer compositions which contain one or more
partially modified vinyl hydroxy ester and/or vinyl hydroxy amide
copolymers (the essential component), and one or more (100 percent)
completely (therefore made by the monomer modification route only)
modified vinyl hydroxy ester and/or vinyl hydroxy amide
homopolymers or copolymers. The satisfactory compositional range is
again defined in terms of mole percent repeat units from all
polymeric sources in the blocking layer composition, i.e. the
amount of all modified repeat units is between about 21 mole
percent and about 75 mole percent. When blocking layer compositions
are selected near the lower modified repeat unit end of the range,
the modified vinyl hydroxy ester and/or vinyl hydroxy amide repeat
unit, in the one or more essential modified copolymers, should
comprise at least about 0.5 mole percent of all the modified repeat
units in the blocking layer composition with the remainder of the
modified repeat units coming from the 100 percent modified
polymeric components. The range for all unmodified repeat units in
the blocking layer composition is preferably between about 25 and
about 79 mole percent. As in all blocking layer compositions of
this invention, at least one of the plurality modified copolymers
comprises between about 21 mole percent and about 75 mole percent
modified repeat units.
(2) Those blocking layer compositions which contain one or more
partially modified vinyl hydroxy ester and/or vinyl hydroxy amide
copolymers (the essential component), and one or more (100 percent)
completely modified vinyl hydroxy ester and/or vinyl hydroxy amide
homopolymers or copolymers, and one or more completely (100
percent) unmodified vinyl hydroxy ester and/or vinyl hydroxy amide
homopolymers or copolymers. Usually each 100 percent polymer in the
previous sentence will be comprised of some of the same repeat
units that make up the essential polymeric component, but this not
always necessarily so. A satisfactory range for all modified repeat
units is between about 0.5 mole percent and about 75 mole percent,
with the modified repeat units in the one or more essential
modified copolymers comprising at least about 0.5 mole percent of
all the modified repeat units in the blocking layer composition.
This restriction is applicable to all the blocking layer
compositions in this invention because the one or more essential
modified copolymers homogenize or compatibilize the totally
modified or totally unmodified homopolymers or copolymers,
resulting in the preferred level of blocking layer miscibility that
allows reproduceable backside exposure and photoreceptor use. When
greater than about 75 percent of the total number of vinyl hydroxy
ester or vinyl hydroxy amide repeat units are chemically modified,
the interlayer mixing problem sets in and causes the electrical
properties of the device to degrade to an undesirable level.
Optimum adhesion improvement is achieved when between about 30 mole
percent and about 50 mole percent of the total number of vinyl
hydroxy ester or vinyl hydroxy amide repeat units in the copolymer
are chemically modified. The polymer blends in the blocking layer
may comprise between about 0.5 mole percent and about 75 mole
percent of chemically modified repeat units and between about 99.5
mole percent and about 25 mole percent nonchemically modified
repeat units, based on all the repeat units in the charge blocking
layer. The weight percent values will vary depending upon what the
hydroxyl modifying unit (O-Z) selected.
Typical optimum adhesive blocking layer compositions containing an
optimum level of modified copolymer and unmodified homopolymer
blends include:
A. 30 mole percent benzoate ester of poly (2-hydroxyethyl
methacrylate) and poly (2-hydroxyethyl methacrylate) [P(HEMA)
benzoate ester+P(HEMA)].
B. 30 mole percent benzoate ester of poly (2-hydroxyethyl
methacrylate) and poly (2-hydroxyethylacrylate) [P(HEMA) benzoate
ester+P(HEA)].
C. 30 mole percent benzoate ester of poly (2-hydroxyethyl acrylate)
and poly (2-hydroxyethyl acrylate) [P(HEA) benzoate
ester+P(HEA)].
D. 30 mole percent benzoate ester of poly (2-hydroxyethyl acrylate)
and poly (2-hydroxyethyl methacrylate) [P(HEA) Benzoate
ester+P(HEMA)].
E. 30 mole percent benzoate ester of poly (2-hydroxypropyl
methacrylate) and poly (2-hydroxyethyl methacrylate) [P(HPMA)
benzoate ester+P(HEMA)].
F. 30 Mole percent benzoate ester of poly (2-hydroxypropyl
methacrylate) and poly (2-hydroxyethyl acrylate) [P(HPMA) benzoate
ester+P(HEA)].
G. 30 mole percent benzoate ester of poly (2-hydroxypropyl
methacrylate) and poly (2-hydroxypropylmethacrylate) [P(HPMA)
benzoate ester+P(HPMA)].
H. 30 mole percent benzoate ester of poly (2-hydroxyethyl acrylate)
and poly (2-hydroxypropyl methacrylate) [P(HEA) Benzoate
ester+P(HPMA)].
I. 30 mole percent benzoate ester of poly (2-hydroxyethyl
methacrylate) and poly (2-hydroxypropyl methacrylate) [P(HEMA)
benzoate ester and P(HPMA)].
The above unmodified homopolymers are mixed with the chemically
modified benzoate ester copolymer, the essential modified copolymer
blocking layer component, in a solution wherein the unmodified
repeat units in the unmodified homopolymer or copolymer comprise in
these optimum blocking layer compositions between about 70 mole
percent and about 95 mole percent and the modified benzoate ester
repeat units in the modified copolymer comprise between about 5
mole percent and about 30 mole percent of all the repeat units in
the blocking layer composition. Such a blocking layer coating is
then fabricated by any suitable conventional process.
Other typical optimum modified copolymer-unmodified homopolymer
blends comprising the blocking layers of this invention include the
30 mole precent benzoate ester of poly (2-hydroxypropyl acrylate)
[P(HPA)] with the unmodified homopolymer poly (2-hydroxypropyl
acrylate) [P(HPA)], or with the unmodified homopolymer poly
(2-hydroxypropyl methacrylate) [P(HPMA)], or with the unmodified
homopolymer poly (2-hydroxyethyl acrylate) [P(HEA)], or with the
unmodified homopolymer poly (2-hydroxyethyl methacrylate)
[P(HEMA)]. It should be understood that the unmodified homopolymer
component could also comprise blends of the above unmodified
homopolymers, or could comprise copolymers or blends thereof
containing the repeat units named in the above unmodified
homopolymers. Similarly the modified copolymer component could also
comprise blends of the above named modified copolymers, and could
contain one or more different modified repeat units and unmodified
repeat units. Similarly, the modified vinyl hydroxy ester and/or
vinyl hydroxy amide copolymers could contain acetate esters or
other esters such as those derived from monofunctional aromatic
carboxylic acid chlorides listed as Z-X" reactants above which
could be blended with unmodified polymers. Also phenylurethanes of
these vinyl hydroxy ester containing polymers may be blended with
unmodified polymers.
Typical unmodified polymers include the numerous unmodified vinyl
hydroxy ester polymers and vinyl hydroxy amide polymers listed
above.
Typical optimum adhesive blocking layer compositions containing
modified copolymer-modified copolymer type blends include:
A. 30 mole percent benzoate ester of poly (2-hydroxyethyl
methacrylate) and 30 mole percent benzoate ester of poly
(2-hydroxyethyl acrylate) [P(HEMA) benzoate ester+P(HEA) benzoate
ester].
B. 30 mole percent benzoate ester of poly (2-hydroxyethyl
methacrylate) and 30 mole percent benzoate ester of poly
(2-hydroxypropyl methacrylate) [P(HEMA) benzoate ester and P(HPMA)
Benzoate ester].
C. 30 mole percent benzoate ester of poly (2-hydroxyethyl
methacrylate) and 30 mole percent acetate ester of poly
(2-hydroxyethyl methacrylate) [P(HEMA) benzoate ester and P(HEMA)
acetate ester].
D. 30 mole percent benzoate ester of poly (2-hydroxyethyl
methacrylate) and 30 mole percent acetate ester of poly
(2-hydroxyethyl acrylate) [P(HEMA) benzoate ester and P(HEA)
acetate ester].
E. 30 mole percent benzoate ester of poly (2-hydroxyethyl acrylate)
and 30 mole percent acetate ester of poly (2-hydroxyethyl acrylate)
[P(HEA) benzoate ester and P(HEMA) acetate ester].
F. 30 mole percent benzoate ester of poly (2-hydroxyethyl
methacrylate) and 30 mole percent acetate ester of poly
(2-hydroxypropyl) methacrylate [P(HEMA) benzoate ester &
P(HPMA) acetate ester].
G. 30 mole percent acetate ester of poly (2-hydroxyethyl
methacrylate) and 30 mole percent benzoate ester of poly
(2-hydroxypropyl methacrylate) [P(HEMA) acetate ester and P(HPMA)
benzoate ester].
H. 30 mole percent acetate ester of poly (2-hydroxyethyl
methacrylate) and 30 mole percent acetate ester of poly
(2-hydroxyethyl acrylate) [P(HEMA) acetate ester and P(HEA) acetate
ester].
I. 30 mole percent acetate ester of poly (2-hydroxyethyl
methacrylate) and 30 mole percent acetate ester of poly
(2-hydroxypropyl methacrylate) [P(HEMA) acetate ester and P(HPMA)
acetate ester].
Other typical optimum adhesive blocking layer compositions
containing modified copolymer-modified copolymer blend combinations
include poly (2-hydroxypropyl acrylate) [P(HPA)] benzoate and
acetate esters combined with P(HEMA), P(HPMA) and P(HEA) benzoate
and acetate esters].
Typical optimum adhesive blocking layer compositions containing
blends involving terpolymers include:
Terpolymer I: Poly [(2-hydroxyethyl methacrylate),
(2-hydroxyethylacrylate), (2-hydroxypropyl
methacrylate)][P(HEMA)+P(HEA)+P(HPMA)] wherein the maximum single
repeat unit content is 80 mole percent and the minimum 10 mole
percent.
Terpolymer II: Same as Terpolymer I, but randomly modified so that
30-50 mole percent of the total repeat unit content is hydroxyl
modified as the benzoate ester.
Terpolymer III: Same as Terpolymer I, but randomly modified so that
30-50 mole percent of the total repeat unit content is hydroxyl
modified as the acetate ester.
Terpolymer IV: Same as Terpolymer I but randomly modified so that
30 mole percent of the total repeat unit content is hydroxyl
modified as the benzoate ester and another 20 mole percent is
modified as the acetate ester.
Terpolymer V: Same as Terpolymer I, but randomly modified so that
30 mole percent of the total repeat unit content is hydroxyl
modified as the benzoate ester and another 20 mole percent is
modified as the phenyl urethane.
The foregoing terpolymers may be mixed in all ten combinations
[e.g. I and II, I and III, I and IV, I and V, II and III, II and
IV, II and V, III and IV, III and V, and IV and VI] with each other
to achieve desired adhesive-blocking layer properties including
insolubility in subsequently used coating compositions, at least
satisfactory peel test adhesion of greater than about 5 g/cm at the
blocking layer-charge generator layer interface, and stable cyclic
electrical properties. Moreover, these terpolymers may also be
combined with any of the previously defined copolymers and
homopolymers to provide the desired adhesive-blocking layer
properties.
MONOFUNCTIONAL ELECTROPHILE
The uncrosslinked vinyl hydroxy ester or vinyl hydroxy amide
polymer may be chemically modified at a nucleophilic hydroxyl group
by any suitable monofunctional electrophile. The expression
"monofunctional electrophile" as employed herein is defined as
either a non-polymeric molecular species which contains one group
[X" as an atom or group of atoms] that is easily displaceable
(usually as the leaving group HX") by the nucleophilic hydroxyl
group of the vinyl hydroxy ester and/or vinyl hydroxy amide
containing polymer or copolymer; or as a non-polymeric molecular
species which contains a site of unsaturation (Z in some examples)
across which is readily added the nucleophilic hydroxyl group of
the vinyl hydroxy ester and/or vinyl hydroxy amide containing
polymer or copolymer to give OZH. The modified copolymer products
of the above described chemical reactions can be used as one of the
essential modified copolymers in the adhesive-blocking layer
compositions of this invention. The same monofunctional
electrophiles may also modify, in like manner, a vinyl hydroxy
ester or a vinyl hydroxy amide monomer which can then be
subsequently polymerized or copolymerized to give a modified
homopolymer or copolymer to be used in the adhesive-blocking layer
compositions of this invention. Typical classes of Z-X" reactants
or monofunctional electrophile modifiers of vinyl hydroxy ester
and/or amide polymers include: carboxylic acid chlorides,
carboxylic acid anhydrides, isocyanates of various kinds, sulfonyl
chlorides, alkyl halides, activated aryl halides, activated esters,
and other active compounds including halides of silicon,
phosphorus, selenium, boron and any other suitably reactive
monofunctional heteroatom halides, and the like. Heteroatoms may
also coexist in these non-cyclic and cyclic reactants in chemically
inert locations of the structural formula. The chemically modified
polymer of this invention should be uncrosslinked and solvent
soluble so that is can be applied as a coating with the aid of a
solvent or, if desired, blended with another polymer. Thus
reactions with difunctional (or higher polyfunctionality) compounds
should be avoided so that the chemically modified polymer does not
crosslink. Z-X" and are Z both considered monofunctional
electrophiles because they both undergo modifying chemical
reactions with nucleophiles, like the hydroxyl group, in vinyl
hydroxy ester and/or vinyl hydroxy amide containing polymers and
monomers. However, the Z reactant can be a monofunctional
electrophile via two different reaction pathways versus the Z-X"
reactant which is a monofunctional electrophile via only one
reaction pathway. In one form of Z monofunctional electrophile, Z
is an unsaturated site in a non-polymeric molecule in which no
leaving group is displaced because the nucleophilic hydroxyl group
adds to, and does not displace the unsaturation site Z; and in the
second form of Z monofunctional electrophile, Z is part of a ring
structure which undergoes ring opening when the nucleophilic
hydroxyl group displaces the Z group. In this case however the
displaced leaving group remains attached to the hydroxyl group and
therefore to the resulting modified copolymer or monomer. With Z-X'
monofunctional electrophiles, the X" leaving group is always split
off from the modified copolymer or monomer.
The Z reactants or monofunctional electrophile modifiers of vinyl
hydroxy ester and/or amide polymers are more diversified than the
Z-X" reactants, and are best classified into two categories: (1)
cyclic or non-cyclic unsaturated compounds, which may or may not
contain heteroatoms in the unsaturated linkage or in chemically
inert locations of the structural formula, that add the
nucleophilic hydroxyl group at the most reactive unsaturated
linkage and (2) carbocyclic and heterocyclic compounds that readily
undergo ring opening reactions at the heteroatom site or elsewhere
in the structural formula of these cyclic compounds. Unsaturated
sites may or may not be involved in the ring opening process
Typical examples of Z-X" reactants or modifiers that undergo
nucleophilic displacement of the X" group by the hydroxyl group in
vinyl hydroxy ester and/or amide polymers include: carboxylic acid
chlorides such as acetyl chloride, benzoyl chloride,
4-biphenylcarbonyl cloride, 4-p-terphenylcarbonyl chloride,
1-naphthoyl chloride, 2-furoyl chloride, 2-thiophenecarbonyl
chloride, 4-pyridinecarbonyl chloride, 4-chloropyridine
hydrochloride, ethyl chloroformate, phenyl chloroformate, acroyl
chloride, methacroyl chloride; carboxylic acid anhydrides such as
acetic anhydride, benzoic anhydride, lauric anhydride, and
trifluoroacetic anhydride; sulfonyl chlorides such as
methanesulfonyl chloride, p-toluenesulfonyl chloride,
2-thiophenesulfonyl chloride and trifluoromethanesulfonyl chloride;
alkyl halides such as allyl chloride, ally bromide, benzyl
chloride, benzyl bromide, methallyl chloride, butyl iodide,
neopentyl iodide, iodoacetic acid, iodoacetonitrile, iodoacetamide,
chloroacetone, 2-chloroacetophenone and N-(bromomethyl)
phthalimide; activated aryl halides such as 2-chlorobenzoxazole,
2-chlorobenzothiazole, 4-chloro-2,6-diaminopyrimidine,
2-chloro-4,6-diamino-1,3,5-triazine, 3-chloro-2,5-dimethylpyrazine;
activated esters such as N-acryloxysuccinlmide, 3-maleimidobenzoic
acid H-hydroxysuccinimide, (2-naphthoxy) acetio acid
N-hydroxysuccinimide and N-hydroxysuccinimidyl acetoacetate; active
nitrogen heterocyclic compounds such as 1-acetylimidazole,
1-(p-toluenesulfonyl) imidazole, 1-(mesitylenesulfonyl) imidazole,
1-(trimethylsilyl) imidazole, 2-trimethylsilyl-1,2,3-triazole,
1-(p-toluenesulfonyl)-2-pyrrolidinone, 1-(trimethylsilyl)
pyrrolidine; halides of silicon such as dimethylphenylsilyl
chloride and numerous other monofunctional Si-Cl compounds; active
compounds of phosphorus such as 1,2-phenylene phosphorochloridate
and 1,2-phenylene phosphorochloridite; active compounds of boron
such as B-bromocatecholborane; active iminium compounds such as
imidoyl halides, imidate salts and iminium salts; miscellaneous
active compounds of selenium; and the like.
Common examples of Z reactants or modifiers that undergo
nucleophilic addition by the hydroxyl group in vinyl hydroxy ester
and/or amide polymers include:
Category (1): butyl isocyanate, phenyl isocyanate, phenyl
isothiocyanate, benzenesulfonyl isocyanate, N,N-dimethylacrylamide,
N-vinylpyrrolidone, acrylonitrile, other sufficiently activated
vinyl and .alpha. and .beta. unsaturated compounds, sulfines such
as N-thionylaniline and sulfenes generated from a sulfonyl chloride
and tertiary amine such as N-sulfonylaniline or methylene sulfene,
and the like.
Category (2): succinic anhydride, phthalic anhydride, maleic
anhydride, isatoic anhydride, N-methylisatoic anhydride, itaconic
anhydride, 2,3-pyridenedicarboxylic anhydride,
methyl-5-norbornene-2,3-dicarboxylic anhydride, 1,8-naphthoic
anhydride, 2-sulfobenzoic acid anhydride, styrene oxide, t-butyl
glycidyl ether, butadiene monoxide, 1,4-butane sultone, 1,3-propane
sultone, 1,8-naphthosultone, .beta. propiolactone,
2-methyl-1,3,2-dioxaborinane, diketene and the like.
Some of the above modifiers will function more effectively, that is
without crosslinking side reactions and at practical modification
reaction rates, for the vinyl hydroxy ester polymers and others for
the vinyl hydroxy amide polymers.
All chemically active modifiers (i.e. reactants Z-X" and Z) towards
the hydroxyl groups in vinylhydroxy ester and/or amide polymers, on
which the polymer hydroxyl group will perform a nucleophilic
displacement or addition reaction, should be monofunctionally pure,
i.e. greater than about 99.9 percent by weight pure. Non-functional
impurities, or impurities that do not react with the hydroxyl
groups in vinyl hydroxy ester and/or vinyl hydroxy amide polymers,
may co-exist with the monofunctional reactant to decrease the
overall reactant purity to much less than 99.9 percent. If
polyfunctional impurities do exist in the reactant composition, the
polyfunctional impurities must be chemically inert under the
applied reaction conditions of the chemical modification process.
Reactive polyfunctional impurities will crosslink, sometimes
immediately and other times over long time periods, the vinyl
hydroxy ester and/or amide polymers producing a non solvent
processable (insoluble) gel. Strenuous reaction conditions (high
temperature for prolonged times) and vigorous catalysts, both or
either of which could promote secondary reactions between
unmodified hydroxyl groups and modified hydroxyl groups to give a
non-processible crosslinked product, should also be avoided.
Hydroxyl group nucleophilic displacement reactions on Z-X"
reactants (modifiers) will generally yield a reaction by product
which itself has been separated from the modifier (usually as HX")
may be volatile or easily washed out of the modified copolymer
during isolation thereof. The by product may be removed in its
native form or may be combined with a (basic) acid scavenger to be
removed as a water soluble organic salt. Hydroxyl group
nucleophilic addition reactions on Z reactants (modifiers)
generally do not afford a reaction by product which facilitates
isolation of pure modified copolymer. In these nucleophilic
addition polymer modification reactions, the hydroxyl hydrogen is
generally transferred to the attached modified hydroxyl group as
-OZH.
Generally, the hydroxyl groups in the polymer are chemically
modified (altered) to the total extent of between about 21 percent
and about 75 percent of the total number initially present in the
polymer prior to chemical modification as described above.
Satisfactory results may be achieved with chemically modified vinyl
hydroxy ester or vinyl hydroxy amide polymers having a number
average molecular weight of at least about 10,000, the upper limit
being limited by the viscosity necessary for processing.
Preferably, the weight average molecular weight is between about
20,000 and about 2,000,000. Optimum blocking layer performance is
obtained when the weight average molecular weight is between about
100,000 and about 2,000,000.
CHEMICAL REACTION FOR PREPARING CHEMICALLY MODIFIED POLYMERS
A typical chemical reaction for preparing chemically modified vinyl
hydroxy ester or vinyl hydroxy amide polymers include:
(1) Nucleophilic Displacement Reactions such as: ##STR8## wherein:
X'" is X without the hydroxyl group(s),
Z-X" is the chemical modifier or modifying agent wherein:
Z is the part of the modifying agent incorporated into the polymer
as OZ in repeat unit B and
X" is the remainder of the modifying agent that is removed
(evaporated or washed out as is or as an organic salt) from the
modification process as HX".
(2) Nucleophilic Addition Reactions such as: ##STR9## wherein: X'
is X without the hydroxyl group(s),
Z is the chemical modifier or modifying agent which is entirely
incorporated into the polymer as OZH in repeat unit B.
Since there is no by product (or leaving group) from this addition
modification reaction, only unreacted modifier (if any exists)
should be removed from the contents of the modification
process.
The uncrosslinked chemically modified polymers of this invention
are solvent soluble. Any suitable solvent may be utilized to apply
the blocking layer. Typical solvents include methanol,
1-methoxy-2-hydroxypropane, tertiary butyl alcohol, water and
mixtures of these solvents with other alcohol solvents and
tetrahydrofuran and the like. Choice of solvents depends upon the
nature of the conductive layer upon which the barrier layer is
applied and also on the properties of the polymers constituting the
blocking layer. Appropriate solvents can, in general, be selected
based on the known properties of the individual polymers, as is
well known in the art. Mixtures of solvents may also be used, if
desired. The proportion of solvent to be utilized varies with the
type of coating technique to be employed, e.g., dip coating, spray
coating, wire wound bar coating, roll coating, and the like so that
the viscosity and volatility of the coating mixture is adjusted to
the type of coating technique utilized. Generally, the amount of
solvent ranges from between about 99.8 percent by weight to about
90 percent by weight, based on the total weight of the coating
composition.
Any suitable and conventional coating technique may be employed to
apply the blocking layer to the underlying surface. Typical
application techniques include spraying, dip coating, roll coating,
wire wound rod coating, and the like. The specific composition
selected for the ground plane will influence the thickness of the
blocking layer selected. Generally, satisfactory results may be
achieved with a dried blocking layer coating having a thickness
between about 0.05 micrometer and about 8 micrometers on some
conductive layers. When the thickness of the layer exceeds about 8
micrometers, the electrophotographic imaging member may show poor
discharge characteristics and residual voltage build-up after erase
during cycling. A thickness of less than about 0.02 micrometer
tends generally to result in pin holes as well as high dark decay
and low charge acceptance due to non-uniformity of the thickness of
different areas of the blocking layer. The preferred thickness
range is between about 0.3 micrometer and about 1.5 micrometers.
Optimum hole blocking results are achieved with a thickness of
between about 0.2 micrometer and about 1 micrometer on non-metallic
electrically conductive layers and between about 0.05 micrometer
and about 1 micrometer on electrically conductive metallic
surfaces. However, the surface resistivity of the dry blocking
layer of the present invention should be greater than about
10.sup.10 ohms/sq as measured at room temperature (25.degree. C.)
and one atmosphere pressure under 40 percent relative humidity
conditions. This minimum electrical resistivity prevents the
blocking layer from becoming too conductive.
After the blocking layer coating is applied, the deposited coating
is heated to drive out the solvent and form a solid continuous
film. Generally, a drying temperature between about 110.degree. C.
and about 135.degree. C. is preferred to minimize any residual
solvent, and to minimize any distortion to organic film substrates
such as biaxially oriented polyethylene terephthalate. The
temperature selected depends to some extent on the specific
electrically conductive layer utilized and is limited by the
temperature sensitivity of the substrate. The drying temperature
may be maintained by any suitable technique such as ovens, forced
air ovens, radiant heat lamps, and the like. The drying time
depends upon the temperatures used. Thus, less time is required
when higher temperatures are employed. Generally, increasing the
drying time increases the amount of solvent removed. One may
readily determine whether sufficient drying has occurred by
chromatographic or gravimetric analysis.
To achieve maximum adhesion between the charge blocking layer and
the charge generating layer, the charge generating polymer binder
solvent selected for applying the charge generation layer should
preferably also at least partially swell the uncrosslinked
chemically modified polymers of this invention to introduce or
promote polymer-polymer interfacial penetration, but not bulk
mixing of the two layers. Thus, the polymers from each layer would
be immiscible if coated from a common solvent mixture when the
charge generating layer is coated on top of the blocking layer.
Only a very small polymer-polymer penetration depth gives improved
adhesion. This amounts to mixing of polymer from each of the
contacting monolayers to form a thin continuous interfacial polymer
mixing zone. Special bonding interactions also play a role in
strengthening adhesive forces in the interfacial polymer mixing
zone. These special bonding interactions are in part created by
hydroxyl group chemical modification of vinyl hydroxy ester and/or
vinyl hydroxy amide containing polymers comprising the blocking
layer. In this invention the special bonding interactions include
hydrogen bonding, dipole-dipole interactions and bonding from
aromatic ring II orbital overlap wherein the latter bonding
interaction is generated by benzoylation (modification) of the
hydroxyl groups in the blocking layer polymer. Preferably, a common
structural feature is shared by the adjacent layer polymers to
provide improved adhesion from the interfacial polymer mixing zone.
The frequency of the common structural feature [e.g. aromatic group
content introduced by benzoylation of the hydroxyl containing
blocking layer polymer to form a benzoate ester (aromatic) group]
in the blocking layer and charge generating layer polymers is
selected (hydroxyl modification fraction in the blocking layer) to
provide an interfacial polymer mixing zone. The thickness of the
thin continuous interfacial polymer mixing zone is preferably
between about 50 angstroms and about 150 angstroms. Thicknesses
greater than about 200 angstroms may lead to cyclic electrical
failure whereas thicknesses less than about 25 angstroms may
exhibit adhesion comparable to embodiments where no interfacial
polymer mixing occurs.
When, for example, there is close structural identity between an
aromatic group (e.g. alkyl benzoate ester group) in a benzoylated
vinyl hydroxy ester of a chemically modified blocking layer polymer
of this invention and an aromatic group (e.g. alkyl benzoate ester
group) in a polyester binder of an adjacent charge generation
layer, an interfacial polymer mixing zone forms between the layers
and a very large adhesion improvement (e.g. from less than about 5
g/cm to greater than about 200 g/cm) is realized. A moderate
adhesion improvement was found where benzene rings were the common
structural identity of polymers in the blocking layer and the
generating layer (e.g. substitution of a benzoylated vinyl hydroxy
ester of a chemically modified blocking layer polymer for a
chemically unmodified blocking layer used in combination with
generating layers containing polyvinyl carbazole improved adhesion
from less than about 5 g/cm to 23 g/cm). For generating layers
containing a polyvinyl butyral binder, the adhesion improvement
increased from less than about 5 g/cm to about 10 g/cm with the
(benzoylated) modified vinyl hydroxy ester blocking layer polymer.
This smaller adhesion improvement is presumably because of the
absence of common structural features in the interfacially mixed
polymers. It is believed that an interfacial zone formed in which
the modified vinyl hydroxy ester polymer from the blocking layer
and the polyvinyl carbazole from the generating layer occurred to
cause the large adhesion improvement observed.
Any suitable solvent may be utilized to apply the generating layer.
Typical solvents include methylene chloride, 1,2-dichloroethane,
1,1,2-trichloroethane, toluene, tetrahydrofuran, cyclohexanone,
methyl ethyl ketone, and the like. Generally, the solvent utilized
to apply the generator layer should swell the surface of the
blocking layer to ensure the formation of an interfacial zone
between the blocking layer and the generating layer, the
interfacial zone containing a mixture of polymers from both the
blocking layer and the generating layer. The expression "swelling"
as employed herein is defined as partial solubility of a cluster of
polymer chains wherein the solvent is not sufficiently strong
enough to surround each individual polymer chain, and so the
solvent only surrounds clusters of polymer chains on all sides or
on less than all sides of the cluster. Thus, only the outside
polymer chains of the cluster in contact with the solvent become
somewhat mobile in their partial dissolution state, but this
mobility is sufficient to cause a significant amount of interlayer
polymer-polymer contact with special bonding interactions, and the
resulting mixing zone wherein the polymer-polymer contact occurs
results in greatly improved adhesion.
Any suitable and conventional coating technique may be employed to
apply the generating layer to the blocking layer.
Generally, as described above and hereinafter, the
electrophotoconductive imaging member of this invention comprises a
supporting substrate layer having an electrically conductive
surface, a vinyl hydroxy ester and/or a vinyl hydroxy amide polymer
(with greater than about 20 mole percent modified repeat units)
containing blocking layer and a photoconductive imaging layer. The
photoconductive layer may comprise any suitable photoconductive
material well known in the art. Thus, the photoconductive layer may
comprise, for example, a single layer of a homogeneous
photoconductive material or photoconductive particles dispersed in
a binder, or multiple layers such as a charge generating overcoated
with a charge transport layer. The photoconductive layer may
contain homogeneous, heterogeneous, inorganic or organic
compositions. One example of an electrophotographic imaging layer
containing a heterogeneous composition is described in U.S. Pat.
No. 3,121,006 wherein finely divided particles of a photoconductive
inorganic compound are dispersed in an electrically insulating
organic resin binder. The entire disclosure of this patent is
incorporated herein by reference. Other well known
electrophotographic imaging layers include amorphous selenium,
halogen doped amorphous selenium, amorphous selenium alloys
including selenium arsenic, selenium tellurium, selenium arsenic
antimony, and halogen doped selenium alloys, cadmium sulfide and
the like.
This invention is particularly desirable for electrophotographic
imaging layers which comprise two electrically operative layers, a
charge generating layer and a charge transport layer.
Any suitable charge generating or photogenerating material may be
employed as one of the two electrically operative layers in the
multilayer photoconductor embodiment of this invention. Typical
charge generating materials include metal free phthalocyanine
described in U.S. Pat. No. 3,357,989, metal phthalocyanines such as
copper phthalocyanine, vanadyl phthalocyanine, selenium containing
materials such as trigonal selenium, bisazo compounds,
quinacridones, substituted 2,4-diaminotriazines disclosed in U.S.
Pat. No. 3,442,781, and polynuclear aromatic quinones available
from Allied Chemical Corporation under the tradename Indofast
Double Scarlet, Indofast Violet Lake B, Indofast Brilliant Scarlet
and Indofast Orange. Other examples of charge generator layers are
disclosed in U.S. Pat. Nos. 4,265,990, 4,233,384, 4,471,041,
4,489,143, 4,507,480, 4,306,008, 4,299,897, 4,232,102 4,233,383,
4,415,639 and 4,439,507. The disclosures of these patents are
incorporated herein by reference in their entirety.
Any suitable inactive resin binder material may be employed in the
charge generator layer. Typical organic resinous binders include
polycarbonates, acrylate polymers, vinyl polymers, cellulose
polymers, polyesters, polysiloxanes, polyamides, polyurethanes,
epoxies, and the like. Many organic resinous binders are disclosed,
for example, in U.S. Pat. Nos. 3,121,006 and 4,439,507, the entire
disclosures of which are incorporated herein by reference. The
photogenerating composition or pigments is present in the resinous
binder composition in various amounts. When using an electrically
inactive or insulating resin, it is essential that there be
particle-to-particle contact between the photoconductive particles.
This necessitates that the photoconductive material be present in
an amount of at least about 15 percent by volume of the binder
layer with no limit on the maximum amount of photoconductor in the
binder layer. If the matrix of binder comprises an active material,
e.g. poly-N-vinylcarbazole, the photoconductive material need only
to comprise about 1 percent or less by volume of the binder layer
with no limitation on the maximum amount of photoconductor in the
binder layer. Generally for charge generator layers containing an
electrically active matrix or binder such as polyvinyl carbazole or
phenoxy resin [poly(hydroxyether)], from about 5 percent by volume
to about 60 percent by volume of the photogenerating pigment is
dispersed in about 40 percent by volume to about 95 percent by
volume of binder, and preferably from about 7 percent to about 30
percent by volume of the photogenerating pigment is dispersed in
from about 70 percent by volume to about 93 percent by volume of
the binder The specific proportions selected also depends to some
extent on the thickness of the generator layer. The thickness of
the photogenerating binder layer is not particularly critical.
Layer thicknesses from about 0.05 micrometer to about 40
micrometers have been found to be satisfactory. The photogenerating
binder layer containing photoconductive compositions and/or
pigments, and the resinous binder material preferably ranges in
thickness of from about 0.1 micrometer to about 5 micrometers, and
has an optimum thickness of from about 0.3 micrometer to about 3
micrometers for best light absorption and improved dark decay
stability and mechanical properties.
The active charge transport layer may comprise any suitable
transparent organic polymer or non-polymeric material capable of
supporting the injection of photo-generated holes and electrons
from the charge generation layer and allowing the transport of
these holes or electrons through the organic layer to selectively
discharge the surface charge. The active charge transport layer not
only serves to transport holes or electrons, but also protects the
photoconductive layer from abrasion or chemical attack and
therefore extends the operating life of the photoreceptor imaging
member. The charge transport layer should exhibit negligible, if
any, discharge when exposed to a wavelength of light useful in
xerography, e.g. 4000 Angstroms to 8000 Angstroms. Therefore, the
charge transport layer is substantially transparent to radiation in
a region in which the photoconductor is to be used. Thus, the
active charge transport layer is a substantially
non-photoconductive material which supports the injection of
photogenerated holes or electrons from the generation layer. The
active transport layer is normally transparent when exposure is
effected through the active layer to ensure that most of the
incident radiation is utilized by the underlying charge carrier
generator layer for efficient photogeneration. The charge transport
in conjunction with the generation layer in the instant invention
is a material which is an insulator to the extent that an
electrostatic charge placed on the transport layer is not
conductive in the absence of illumination, i.e. does not discharge
at a rate sufficient to prevent the formation and retention of an
electrostatic latent image thereon.
The active charge transport layer may comprise an activating
compound useful as an additive dispersed in electrically inactive
polymeric materials making these materials electrically active.
These compounds may be added to polymeric materials which are
incapable of supporting the injection of photogenerated holes from
the generation material and incapable of allowing the transport of
these holes therethrough. This will convert the electrically
inactive polymeric material to a material capable of supporting the
injection of photogenerated holes from the generation material and
capable of allowing the transport of these holes through the active
layer in order to discharge the surface charge on the active
layer.
An especially preferred transport layer employed in one of the two
electrically operative layers in the multilayer photoconductor
embodiment of this invention comprises from about 25 to about 75
percent by weight of at least one charge transporting aromatic
amine compound, and about 75 to about 25 percent by weight of a
polymeric film forming resin in which the aromatic amine is
soluble. These charge transporting materials are well known in the
art as are the binders and techniques for applying the layers.
Generally, the thickness of the transport layer is between about 5
micrometers to about 100 micrometers, but thicknesses outside this
range can also be used. In general, the ratio of the thickness of
the charge transport layer to the charge generator layer is
preferably maintained from about 2:1 to 200:1 and in some instances
as great as 400:1.
If desired, the charge transport layer may comprise any suitable
electrically active charge transport polymer instead of a charge
transport monomer dissolved or dispersed in an electrically
inactive binder. Electrically active charge transport polymer
employed as charge transport layers are described, for example in
U.S. Pat. Nos. 4,806, 443, 4,806,444, and 4,818,650, the entire
disclosures thereof being incorporated herein by reference.
Optionally, an overcoat layer may also be utilized to improve
resistance to abrasion. In some cases a back coating may be applied
to the side opposite the photoreceptor to provide flatness and/or
abrasion resistance. These overcoating and backcoating layers may
comprise organic polymers or inorganic polymers that are
electrically insulating or slightly semi-conductive as is well
known in the art.
A number of examples are set forth hereinbelow and are illustrative
of different compositions and conditions that can be utilized in
practicing the invention. All proportions are by weight unless
otherwise indicated. It will be apparent, however, that the
invention can be practiced with many types of compositions and can
have many different uses in accordance with the disclosure above
and as pointed out hereinafter.
EXAMPLE 1
Chemical Modification of A Vinyl Hydroxy Ester Containing
Polymer
Part A: Chemical Modification of Poly (2-hydroxyethyl methacrylate)
With Benzoyl Chloride
To a 3 liter 3-neck round bottom flask equipped with a mechanical
stirrer, argon inlet and outlet tube, and a water condenser was
charged 2000 grams of N,N-dimethylformamide (solvent), 87.3 grams
(0.863 mole) triethylamine (acid scavenger) and 19.54 grams (0.160
mole) 4 dimethylaminopyridine (catalyst). To this rapidly stirred
solution at room temperature and under an argon flow was added, 200
grams [1.54 mole of poly (2-hydroxyethyl methacrylate) P(HEMA)
repeat units] of high molecular weight P(HEMA), and after 5 hours
stirring a viscous P(HEMA) solution (.about.9 weight percent)
remained. The unmodified P(HEMA) had a Mw of
1.0-1.4.times.10.sup.6, and an intrinsic viscosity [.eta.] of about
0.65 dl/g measured in methanol at 25.degree. C., and was obtained
from Scientific Polymer Products. The unmodified P(HEMA) had an
intrinsic viscosity in the range of 1.85-2.15 dl/g (wherein the
intrinsic viscosity was obtained in dimethylformamide solvent at
30.degree. C.). The viscosity average molecular weight for this
intrinsic viscosity range is about 955,000 to 1,180,000 as obtained
from the Mark-Houwink relationship in which the constants are
K=8.9.times.10.sup.-5 and a=0.72. The viscosity average molecular
weight is generally about 10 percent less that the weight average
molecular weight at a given intrinsic viscosity value, and the
weight average molecular weight is generally 2 to 3 times the
number average molecular molecular weight.
To the stirred viscous polymer solution at room temperature was
dropwise added 110.29 g (0.785 mole) of benzoyl chloride and the
resulting solution was allowed to stir under ambient conditions
overnight. Finally the polymer solution was coagulated into 10
liters of mechanically stirred deionized water. The precipitated
polymer was filtered and then slurried several times with deionized
water until the final filtrate had a low conductivity value
(.ltoreq.50 micromhos or microsiemens) as measured with a model II
Nester Micromho Pen.TM.. The moist modified copolymer was dried at
40.degree. C. overnight in either an air convection oven or a
vacuum oven at about 0.5 mm Hg. .sup.1 H-NMR analysis of the dried
modified polymer was obtained in DMSO-d.sub.6 solution (5 weight
percent) using a Bruker AM-360 system equipped with a 5 mm QNP
probe. Proton data were accumulations of 16 transients at room
temperature, using a recycle delay between 30 degree pulses of 4.5
seconds total. A trace amount of tetramethylsilane was added to the
NMR solution as an internal standard (chemical shift reference).
The average modified and unmodified repeat unit content per polymer
chain was calculated from a direct comparison between the
normalized signal intensities of the benzoate ester phenyl group
(7.4-8.1 ppm multiplet) in the modified P(HEMA) repeat units, and
the hydroxyl hydrogen (4.75 ppm singlet) in the unmodified P(HEMA)
units. In this modification reaction, the average P(HEMA) benzoate
ester content was about 30-31 percent of the total repeat units per
polymer chain which indicates about 60 mole percent of the charged
benzoyl chloride became attached to the P(HEMA)hydroxyl groups. The
other 40 mole percent of charged benzoyl chloride was consumed by
the (about 3 weight percent) water present in the unmodified
P(HEMA) used as the starting material in this polymer modification
reaction. Reaction by products, excess reactants, and catalyst were
removed in the deionized water slurries.
Part B: Chemical Modification of Poly (2-hydroxyethyl methacrylate)
With Acetic Anhydride
To a 3 liter 3 neck round bottom flask equipped with a mechanical
stirrer, argon inlet tube and outlet tube, and a water condenser
was charged 1500 grams of N,N-dimethylformamide solvent, 40.58
grams (0.40 mole) triethylamine and 9.77 grams (0.08 mole) of
4-dimethylaminopyridine. The reaction vessel was transferred to a
water bath at 50.degree. C. and with rapid stirring under an argon
flow, 100 g (0.68 mole repeat units) of high molecular weight
P(HEMA) [same P(HEMA) as described in Part A] was added and allowed
to dissolve in about 4 hours.
To the stirred warm viscous polymer solution was dropwise added
40.84 grams (0.40 mole) of acetic anhydride and the resulting
solution was stirred overnight at 50.degree. C. Finally the polymer
solution was coagulated into 10 liters of mechanically stirred
deionized water. The precipitated polymer was filtered and was then
slurried several times with deionized water until the final
filtrate had a low conductivity value (.ltoreq.50 micromhos or
microsiemens) as measured in Part A. The moist modified polymer was
dried at 40.degree. C. overnight in either an air convection oven
or a vacuum oven at 0.5 mm Hg. A .sup.1 H-NMR spectrum was obtained
as in Part A. The average modified and unmodified repeat unit
content per polymer chain was calculated from a direct comparison
between the normalized signal intensities of the acetate ester
methyl group (2.04 ppm singlet) in the modified P(HEMA) repeat
units, and the hydroxyl hydrogen (4.78 ppm singlet) in the
unmodified P(HEMA) repeat units. In this chemical modification
reaction, the average P(HEMA) acetate ester content was about 53
percent of the total repeat units per polymer chain. Since the
charged stoichiometry was for a 72 percent modification level, the
NMR analysis is in excellent agreement. Unlike Part A, in which a
reactive carboxylic acid chloride was used, the less reactive
anhydride is not sacrificed to P(HEMA) bound water and the
anticipated modification level results. As in part A, product
impurities are removed in the deionized water slurries.
Part C: Chemical Modification of Poly (2-hydroxyethyl methacrylate)
With Phenylisocyanate.
To a 1 liter 3 neck round bottom flask equipped with a mechanical
stirrer, argon inlet tube and outlet tube, and a water condenser
was added 400 grams of N,N-dimethylformamide solvent. The reaction
vessel was transferred to a water bath at 50.degree. C. and with
rapid stirring under an argon flow, 50 grams (0.384 mole repeat
units) of high molecular weight P(HEMA) [same P(HEMA) as described
in Part A] was added and allowed to dissolve in about 4 hours at
50.degree. C.
To the stirred warm viscous polymer solution was dropwise added
45.8 grams (0.384 mole) of phenyl isocyanate and the resulting
solution was stirred for 4 hours at 50.degree. C. Finally the
polymer solution was coagulated into 4 liters of mechanically
stirred deionized water. The precipitated polymer was filtered and
was then slurried several times with deionized water until the
final filtrate had a low conductivity value (.ltoreq.50 micromhos
or microsiemens) as measured in Part A. The moist modified polymer
was dried at 40.degree. C. overnight in either an air convection
oven or a vacuum oven at 0.5 mm Hg. A .sup.1 H-NMR spectrum was
obtained as in Part A. The average modified and unmodified repeat
unit content per polymer chain was calculated from a direct
comparison between the normalized signal intensities of the phenyl
urethane group (6.8-7.9 ppm multiplet) in the chemically modified
P(HEMA) repeat units, and the hydroxyl hydrogen (4.81 ppm singlet)
in the unmodified P(HEMA) repeat units. In this modification
reaction, the average P(HEMA) phenyl urethane content was about 70
percent of the total repeat units per polymer chain. Since the
charged stoichiometery was for a 100 percent modification level,
about 30 mole percent of the charged isocyanate was sacrificed to
presumably P(HEMA) bound H.sub.2 O (about 4 weight percent). Karl
Fisher analysis for P(HEMA) water content, as delivered from the
vendor, was commonly about 3-4 weight percent.
EXAMPLE II
This experiment demonstrates that both useful cyclic electrical
properties and improved peel strength adhesion can be obtained in
devices containing P(HEMA) blocking layers that have been doped
with the 30 mole percent P(HEMA) benzoate ester copolymer versus
the same devices in which dopant was omitted. The devices consisted
of polyester (Mylar.TM., available from E. I. duPont de Nemours
& Co.) substrate, a semi-transparent sprayed carbon
black-binder conductive layer, the doped P(HEMA) blocking layer, a
charge generating layer containing vanadyl phthalocyanine particles
dispersed in polyester (Vitel PE-100 resin, available from
Goodyear) and a 25 micrometers thick charge transport layer
consisting of 40 weight percent N,N'-bis (3"
methylphenyl)-[1,1'-biphenyl]-4,4" diamine in polycarbonate
(Makrolon 5705, available from from Farbenfabricken Bayer A. G.).
All the layers were drawbar coated except for the conductive
layer.
The carbon black dispersion for spray fabrication of the conductive
layer was prepared by first dissolving 13.2 grams of methyl
acrylamidoglycolate methyl ether--vinylpyrrolidone copolymer and
13.2 grams of a methyl acrylamidoglycolate methyl
ether--vinylacetate copolymer in 97 grams DMF and 49 grams Dowanol
PM. Then 6.75 grams of N,N'-bis (3" hydroxyphenyl)-[1,1'
biphenyl]-4,4" diamine was dissolved in the above solution. Finally
8.25 grams carbon black (C-975 ultra, available from Columbian
Chemicals Co.) and 500 grams stainless steel shot were added and
the mixture was roll-milled for 5 days to produce a carbon black
dispersion. After filtering the dispersion through a 28 micrometer
Nitex nylon filter cloth and diluting with 90 grams tetrahydrofuran
and 95 grams Dowanol PM, the diluted dispersion was sprayed in one
pass onto the corona treated polyester substrate sheet mounted on a
rotating metal drum. The solvent moist coating was dried for one
hour at 135.degree. C. in an air convection oven and had a
resistivity of about 10 ohms/square. Next blended blocking layer
solutions comprising P(HEMA) and the 30 mole percent P(HEMA)
benzoate ester modified copolymer, prepared by modifying the
unmodified high molecular weight P(HEMA) described in Part A of
Example I, were prepared in Dowanol PM at 2 weight percent and 4
weight percent. These solutions were each drawbar coated onto the
previously described conductive layers using a 0.5 mil drawbar gap
to give dried blocking layer thicknesses of 0.2-0.4 and 0.5-0.7
micrometer respectively. The blocking layers were dried in an air
convection oven for 1 hour at 110.degree. C. Next a charge
generator layer (CGL) dispersion was formulated and attrited on a
large scale and was sampled as needed to drawbar coat charge
generator layers in various photoreceptor devices in this Example.
A solution of 233 grams polyester (Vitel PE-100 resin, available
from Goodyear) and 3793 grams of methylene chloride was prepared by
roll milling the mixture for at least 90 minutes in a 5 gallon
polypropylene carboy. Using a slight positive pressure, this
solution was filtered through a 0.2 micrometer millipore disposable
filter. About 2,300 grams of the filtered polymer solution and
125.5 grams of vanadyl phthalocyanine pigment were mixed in a 1
gallon wide mouth plastic jug using a Tekmar Dispax Mixer (type T45
DPX 56) for about 10 minutes. Next this crude dispersion and an
additional 700 grams of the above polymer solution used to flush
the Dispax Mixer were added to the Union Process Attritor (Model
Is) along with 2200 grams of 1,2-dichloroethane. The contents of
the attritor were covered with aluminum foil sheeting to reduce
solvent evaporation and the attritor was run at 180 RPM for 3 hours
while running cold tap water through the attritor cooling jacket.
The cooling maintained the dispersion at about 15.degree. C. After
3 hours attriting, the attritor speed was reduced to 40 RPM and the
drain valve was opened to empty the solution into a 2 gallon light
tight plastic jug. The closed attritor was briefly rinsed with 1026
grams of the above polymer solution and 344 grams
1,2-dichloroethane. After agitating for 2 minutes at 180 RPM, the
attritor speed was decreased to 40 RPM and the residual dispersion
was flushed into the 2 gallon light tight plastic jug. The entire
vanadyl phthalocyanine dispersion was roll mill for 15-30 minutes
prior to drawbar coating a portion thereof. This dispersion
contains about 5.35 weight percent solids, 3.48 percent of which is
dissolved polyester (PE-100) and 1.87 percent dispersed vanadyl
phthalocyanine. The vanadyl phthalocyanine comprises 35 weight
percent of the dried coating after solvent removal and the solvent
composition is 60 weight percent methylene chloride and 40 weight
percent 1,2 dichloroethane. The dispersion was drawbar (0.5 mil
gap) coated onto the dried blended P(HEMA) blocking layer and the
solvent moist generating layer was dried in an air convection oven
at 100.degree.-110.degree. C. for 1 hour. Finally the charge
transport layer was formulated, coated and dried. To 183.5 grams
methylene chloride was added 20 grams (60 weight percent solids) of
polycarbonate (Makrolon 5705) and the mixture was magnetically
agitated in a 32 oz amber glass bottle until a solution formed
(24-36 hrs). To this solution was added 13.35 grams (40 weight
percent solids) of the hole transport molecule,
N,N'-bis(3"methylphenyl)-[1,1'-biphenyl]-4,4"diamine and the
mixture was stirred for an additional 24 hours. This charge
transport layer solution was drawbar coated (3 mil bar gap) onto
the dried generating layer and the wet coating was briefly (about
0.5 hour) dried at room temperature and then in an air convection
oven, wherein the temperature was gradually increased from room
temperature to 110.degree. C. over 1 hour and was then held at
110.degree. C. for 0.5-1.0 hours. The transport layer dry thickness
was 25.+-.5 micrometers.
The completed photoreceptor was charge-erase cycled using a cyclic
scanner having a single wire corotron (5 cm wide) set to deposit
14.times.10.sup.-8 coulombs/cm of charge on the surface of these
devices. The devices were grounded to an aluminum drum having a
63.1 cm circumference and the drum was rotated at a speed of 20 rpm
to produce a surface speed of 8.3 inches per second and a cycle
time of about 3 seconds. The devices were discharged (erased) with
a short arc xenon lamp white light source (about 3000 ergs
intensity) emitted through a fiber optic light pipe. In two tests,
cutoff-filters (550 and 450 nanometers) were introduced at the
erase lamp source to remove the short wavelength emission. The
entire xerographic simulation (charge and erase) was carried out in
an environmentally controlled light tight chamber. The devices in
the following Table IB were charge-erase cycled for 200 cycles at
ambient conditions (35 percent RH and 20.degree. C.), and the
cyclic electrical properties are indicated for different blending
levels of the 30 mole percent P(HEMA) benzoate ester copolymer in
the P(HEMA) blocking layer. Table IA describes the compositional
variables of the blended blocking layers of this example.
TABLE IA ______________________________________ BLENDED
ADHESIVE-BLOCKING LAYER COMPOSITIONS.sup.a BLENDED BLOCKING LAYER
Modified Unmodified Peel Test P(HEMA) P(HEMA) Device Adhesion
Copolymer Homopolymer No. (g/cm) (wt. %) (wt. %)
______________________________________ 1 <5 0.0 100.0 2 20-25
10.0 90.0 3 & 4 50-100 20.0 80.0 5 & 6 >200 35.0 65.0 7
>200 50.0 50.0 ______________________________________ TOTAL
REPEAT UNITS IN BLOCKING LAYER Device Modified Unmodified No. (wt
%) (Mole %) (wt %) (Mole %) ______________________________________
1 0.0 0.0 100.0 100.0 2 4.4 2.5 96.6 97.5 3 & 4 8.7 5.0 91.3
95.5 5 & 6 15.2 9.1 84.8 90.9 7 21.8 13.4 78.2 86.6
______________________________________ .sup.a All modified
copolymers in these blocking layer compositions are 7 mole percent
(56.45 wt. %) unmodified P(HEMA) repeat units and 30 mole percent
(43.55 wt. %) P(HEMA) repeat units that have been modified with
benzoyl chloride as in Example IA. .sup.b Modified repeat units
originate only from the modified copolymer defined in footnote a.
.sup.c Unmodified repeat units originate from the modified
copolymer in footnote a (from the repeat units that did not undergo
modification) and from all the repeat units in the unmodified
P(HEMA) homopolymer.
Excellent adhesion (device 2) was obtained when as little as 2.5
out of every 100 repeat units in the blocking layer composition
were modified as described in Part A of Example I. This large
adhesion improvement for so small a number of modified repeat units
suggests that modified copolymers, containing the modified repeat
units, aggregate at the surface of the blocking layer during
coating thereof, and that a special interfacial II bonding
interaction may be occurring between the benzene rings of the
modified P(HEMA) copolymer of the blocking layer and the benzene
rings of the PE-100 polyester binder in the charge generating
layer.
TABLE IB ______________________________________ ADHESIVE BLOCKING
LAYER ELECTRICAL PROPERTIES ______________________________________
Peel BLENDED BLOCKING LAYER Test Wt. % Modified Wt. % Unmodified
Device Adhesion P(HEMA) P(HEMA) No. (g/cm) Copolymer Homopolymer
______________________________________ 1 <5 0 100 2 20-25 10 90
3 50-100 20 80 4 50-100 20 80 5 >200 35 65 6 >200 35 65 7
>200 50 50 ______________________________________ Blocking Layer
CYCLIC Device Thickness.sup.d ELECTRICAL PROPERTIES.sup.e No.
(micrometers) Vo(I) Vo(200) Vr(I) Vr(200)
______________________________________ 1 0.35-0.55 1040 1110 8
.sup. 63.sup.a 2 0.2-0.4 1471 1641 25 .sup. 86.sup.b 3 0.2-0.4 1459
1431 27 13 4 0.5-0.7 300 1288 30 13 5 0.2-0.4 1525 1377 32 23 6
0.5-0.7 1385 1300 30 17 7 0.5-0.7 1174 1111 31 24
______________________________________ .sup.a 550 nm cutoff filter
used with erase lamp. .sup.b 450 nm cutoff filter used with erase
lamp. .sup.c Charge generating layer pigment binder ratio same but
total solids level 50 percent of Devices 2-7. .sup.d Thickness of
blocking layer has no significant effect on the peel test adhesion.
.sup.e These 200 cycle electrical properties are satisfactory for
normal imaging processes.
The cyclic electrical data indicate sufficient hole blocking
capability (high V.sub.o) for these blended blocking layers,
comparable to the 100 percent P(HEMA) blocking layer and much
improved versus the same devices without a blocking layer which
only charge to about 600 volts. The photodischarge process to low
residual voltage (V.sub.r) is sufficiently complete when no cutoff
filter is used with the erase lamp. Presumably the erase lamp
cutoff filter diminishes the light intensity level to <3000 ergs
allowing residual charge (photodischarged electrons) to become
trapped in the device causing the observed Vr cycle-up.
The peel test adhesion in Table I was measured at an angle of
180.degree. in the reverse peel test mode. Peel strength was
measured on an Instrumentors Inc. Model SP-102C-3M90 Peel Tester.
The instrument consisted of a calibrated load cell and moving
platen with controlled variable speed. The instrument measured the
force required to separate layers of a multilayer device. Since
this force is a function of peel angle, all measurements were made
with the angle at 180.degree.. The electronic functions of the test
equipment average the force measurements during the time the platen
is moving and displays the average number on a digital meter. The
instrument was calibrated to measure force in gram units. Also,
since the peel strength is dependent on sample size, the force is
divided by the sample width. Thus, peel strengths are reported as
grams per cm. Test samples were prepared each approximately 1 cm
wide by 25 cm long. The coating was partially stripped from the
substrate and mounted on the platen with the substrate surface
attached to the platen and the partly removed end placed in a clamp
connected to a load cell. The platen was equipped with an adhesive
material to firmly hold each sample. For normal peel tests, the
coated layers were pulled from the substrate. For reverse peel
tests, the coated side of the device was placed on the platen
(coated side down) and the substrate was pulled from the coated
layers. The platen speed used for these measurements was 1 inch per
minute and the measurement time was 25 seconds.
The normal peel test values, indicative of delamination at the
charge transport layer-charge generating layer interface, were
always>or equal to 20 g/cm and, therefore, needed no
improvement. The improvement in adhesion between the blocking layer
and adjacent charge generating layer was large when as little as 10
weight percent of the 30 mole percent modified P(HEMA) benzoate
ester copolymer was blended with 90 weight percent unmodified
P(HEMA). This large improvement in adhesion with only 10 weight
percent of the 30 mole percent modified P(HEMA) benzoate ester
copolymer in 90 weight percent unmodified P(HEMA) indicates a
selective migration of the benzoate ester polymer to the blocking
layer surface because the total benzoate ester repeat unit content
in the blocking layer is very low at about 2.5 mole percent.
Blocking layer surface enrichment of the benzoate ester polymer
such that at least about 21 percent of the total polymeric repeat
units at the blocking layer surface are the modified benzoate ester
repeat units is desirable for optimizing adhesion improvement
because in Example III the 20 mole percent modified P(HEMA)
benzoate ester copolymer alone failed to adhere significantly to
the same charge generating layer. The 20 mole percent modified
P(HEMA) benzoate ester copolymer must have about 20 mole percent of
the modified benzoate ester repeat units at the blocking layer
surface since this blocking layer composition comprises a single
polymer component and thus significant selective migration and
aggregation of modified copolymer cannot occur at the blocking
layer surface.
EXAMPLE III
The purpose of this Example is to identify the minimum repeat unit
content of P(HEMA) benzoate ester in the modified P(HEMA) copolymer
(Example I; part A) required to improve blocking layer adhesion to
the vanadyl phthalocyanine/polyester charge generating layer
composition of photoreceptor devices. The devices consisted of a
polyester substrate (Mylar), the same sprayed carbon black
conductive layer composition described in Example II, various
modification levels of chemically modified compositions of P(HEMA)
coated from 3 weight percent solutions to give dried blocking layer
thicknesses of about 0.35-0.55 micrometer, the same vanadyl
phthalocyanine/polyester charge generating layer as Example II
except at 50 weight percent of the solids level and the same charge
transport composition described in Example II. All the layers were
coated and dried as described in Example II.
The completed devices were electrically tested as described in
Example II except a 550 nm short wavelength cutoff filter was
routinely used with the erase lamp except for the 30 mole percent
P(HEMA) benzoate ester modified copolymer blocking layer devices
which were tested with and without the cutoff filter. The devices
in the following Table II were charge-erase cycled for 200 cycles
at ambient conditions (35 percent RH and 20.degree. C.), and the
cyclic electrical properties are indicated for blocking layers
containing different modified copolymer levels of benzoate ester
alone or blended with P(HEMA). Table IIA describes the
compositional variables of the blocking layers of this example.
TABLE IIA ______________________________________ ADHESIVE-BLOCKING
LAYER COMPOSITIONS P(HEMA) Copolymer Modified Unmodified Peel Test
Modification P(HEMA) P(HEMA) Device Adhesion Level.sup.b
Copolymer.sup.c Homopolymer No. (g/cm) (mole %) (wt. %) (wt. %)
______________________________________ 1 0.7 0.0 0.0 100.0 2 2.6
10.0 100.0 0.0 3 2.9 10.0 50.0 50.0 4 3.6 20.0 100.0 0.0 5 4.4 20.0
50.0 50.0 6 <200.sup.a 30.0 100.0 0.0 7 167.sup.a 30.0 50.0 50.0
______________________________________ TOTAL REPEAT UNITS IN
BLOCKING LAYER Device Modified.sup.d Unmodified.sup.e No. (wt %)
(Mole %) (wt %) (Mole %) ______________________________________ 1
0.0 0.0 100.0 100.0 2 16.7 10.0 83.3 90.0 3 8.3 4.8 91.7 95.2 4
31.1 20.0 69.0 80.0 5 15.5 9.3 84.5 90.7 6 43.6 30.0 56.4 70.0 7
21.8 13.4 78.2 86.6 ______________________________________ .sup.a
Cohesive failure in carbon black polymer conductive layer; other
delaminations are adhesive at the blocking layer generator layer
interface. .sup.b Average benzoate ester repeat unit content per
P(HEMA) polymer chain. .sup.c All modified copolymers in these
blocking layer compositions have been synthesized by the benzoyl
chloride modification of P(HEMA) as described in Example IA. .sup.d
Modified repeat units originate only from the modified copolymers
described in footnote c. .sup.e Unmodified repeat units originate
from the modified copolymer in footnote c (from the repeat units
that did not undergo modification) and from all the repeat units in
the unmodified P(HEMA) homopolymer.
TABLE IIB ______________________________________ ADHESIVE-BLOCKING
LAYER ELECTRICAL PROPERTIES ______________________________________
P(HEMA) Copolymer Modified Unmodified Peel Test Modification
P(HEMA) P(HEMA) Device Adhesion Level.sup.b Copolymer.sup.c
Homopolymer No (g/cm) (mole %) (wt. %) (wt. %)
______________________________________ 1 0.7 0.0 0.0 100.0 2 2.6
10.0 100.0 0.0 3 2.9 10.0 50.0 50.0 4 3.6 20.0 100.0 0.0 5 4.4 20.0
50.0 50.0 6 >200.sup.a 30.0 100.0 0.0 6 >200.sup.a 30.0 100.0
0.0 7 167.sup.a 30.0 50.0 50.0 7 167.sup.a 30.0 50.0 50.0
______________________________________ Device No. V.sub.o (1)
V.sub.o (200) V.sub.r (1) V.sub.r (200)
______________________________________ 1 1040 1110 8 63 2 1235 1377
25 151 3 1199 1305 18 119 4 1173 1295 24 120 5 1105 1143 19 91 6
939 815 19 43 6 951 711 20 .sup. 24.sup.c 7 976 925 15 42 7 984 834
13 .sup. 10.sup.c ______________________________________ .sup.a
Cohesive failure in carbon blackpolymer conductive layer; other
delaminations are adhesive at the blocking layer generator layer
interface. .sup.b Average benzoate ester repeat unit content per
P(HEMA) polymer chain. .sup.c V.sub.r lower without 550 nm cutoff
filter; all other devices have 550 nm cutoff filter
The improvement in adhesion for devices 6 and 7 versus devices 1-5
was large because the P(HEMA) benzoate ester modified repeat unit
content in the modified copolymer was increased to 30 mole percent
of the repeat units in the modified copolymer. This very large
increase in blocking layer-charge generating layer adhesion in
device 7 suggests selective migration of the benzoate ester
modified copolymer to the blocking layer surface may be occurring
while drying the blocking layer. However, the unblended 30 mole
percent benzoate ester modified copolymer blocking layer device (6)
also provides improved adhesion at the blocking layer-charge
generating layer interface, and selective modified copolymer
migration is impossible in this single component bulk homogeneous
blocking layer. Thus, if the P(HEMA) benzoate ester modified repeat
unit content is sufficient as in device 6, more than satisfactory
adhesion at the blocking layer-charge generating layer interface is
obtainable with either blended or unblended blocking layers.
Excellent hole blocking was obtained for all devices in Table II as
evidenced by the high V.sub.o (1 and 200) values. However the use
of the 550 nm cutoff filter contributes to V.sub.r cycle-up which
is most obvious for device 1 wherein the blocking layer [100
percent P(HEMA)] is known not to cycle-up significantly on stable
carbon black conductive layers, e.g. see EP 0 448 780 A1 to Spiewak
et al, published Oct. 10, 1991. Comparing the cyclic electrical
results of devices 6 and 7, with and without the erase lamp cutoff
filter, indicates significant changes in V.sub.r result when the
cutoff filter is omitted thus verifying that the cutoff filter
contributes to V.sub.r cycle-up. The larger V.sub.r cycle-up for
devices 2-5 implies electron trapping impurities reside in the 10
and 20 mole percent P(HEMA) benzoate ester blocking layer
compositions. However since blocking layer-generating layer
adhesion is poor in these devices, this result is
insignificant.
EXAMPLE IV
The use of metallic conductive layers and generator layers
containing trigonal selenium particles dispersed in poly
vinylcarbazole with the 30 mole percent modified P(HEMA) benzoate
ester copolymer alone as blocking layer also provided an
electrically useful device with improved adhesion at the blocking
layer-generating layer interface. The device consisted of a
titanized Mylar conductive substrate onto which was drawbar (0.5
mil gap) coated a 6 weight percent Dowanol PM solution of the 30
mole percent P(HEMA) benzoate ester modified copolymer. The
blocking layer was dried at 110.degree. C. for 1 hour to form a
layer 0.8-1 micrometer thick. The blocking layer was next coated
with a charge generator layer dispersion. The charge generator
layer mixture was prepared by forming a dispersion of about 8.57 g
trigonal selenium particles doped with about 1-2 percent by weight
sodium hydroxide, 16.72 g polyvinylcarbazole, 4.93 g
N,N'-bis-(3"methylphenyl)-[1,1'-biphenyl]-4,4'diamine, 100.55 g
tetrahydrofuran and 100.55 g toluene. This dispersion was then
diluted with an equal weight of toluene. The diluted dispersion was
next agitated on a wrist shaker for about 5 minutes immediately
prior to coating the conductive layer with a 1 mil drawbar gap. The
charge generator layer coating was next dried for one hour at room
temperature and for one hour at 100.degree. C. in an air convection
oven. The dry thickness of the photogenerator layer thus obtained
was about 1.0.+-.0.3 micrometer. Finally the charge transport layer
was formulated, coated, and dried as in Example II. The device was
peel tested and charge-erase tested as described in Example II for
200 cycles at ambient conditions (35 percent RH and 20.degree. C.).
The peel test adhesion at the blocking layer-generating layer
interface was found to be about 23 g/cm with the delamination
occurring at the conductive layer-blocking layer interface
indicating the blocking layer-generating layer interface to be even
stronger. The cyclic electrical properties were excellent: V.sub.o
(I) 1320 volts, V.sub.o (200) 1310 volts, V.sub.r (1) 42 volts, Vr
(200) 45 volts.
Another device was drawbar coated on a conductive titanized Mylar
substrate. The blocking layer (0.2 to 0.4 micrometer) was drawbar
coated (0.5 mil gap) from a 2 weight percent Dowanol PM solution
containing 90 weight percent P(HEMA) and 10 weight percent of the
30 mole percent modified P(HEMA) benzoate ester copolymer. Charge
generator and transport layers were drawbar coated as described in
Example 2 using the same formulation, coating and drying
conditions. The device was electrically tested (200 cycles) as
described in Examples II and III, and was also charge-erase cycled
using a motionless scanner at 33 percent RH and 21.degree. C. for
3000 cycles. For motionless scanner testing, a gold film dot (about
150 .ANG. thick) of 0.315 cm.sup.2 area was vacuum deposited on the
surface of the device as the top electrode. The device was charged
to its voltage in the dark by connecting the top gold electrode and
the bottom ground plane (conductive layer) to a DC power supply
(Trek 609A). The charging time was controlled by a relay in series
with the DC power supply. The surface voltage of the device was
measured by a capacitance coupled voltage probe (Trek 565
electrostatic voltmeter and probe). After charging, the device was
erased form the top surface by a white light flash lamp (1538A
Strobotac from General Radio) and no cutoff filter was used to
adjust wavelength exposure and overall intensity. The DC power
supply, relay and the flash lamp were interfaced to and remote
controlled by a personal computer. The cycling test was performed
by repeating the charge-erase step monitored by the personal
computer. The device in this Example was charged by passing a
constant current, equivalent to 155 ncoulombs/cm.sup.2, provided by
the DC power supply for 200 msec. The device was then allowed to
remain in the dark and was erased later. The total cycle time was
2.84 sec/cycle.sup.a. The V.sub.o value was the voltage directly
after charging and the residual voltage (V.sub.r) after erase. The
following table summarizes the cyclic charge-erase data for the
described device when tested by both scanners.
TABLE III ______________________________________ Scanner Mode
(charging Method) x cycles Vo(1) Vo(x) Vr(1) Vr(x)
______________________________________ Motion.sup.a 200 1128 1450
11 123.sup.b (corotron) Motionless 3000 930 1043 48 49.sup.c
(electrode) ______________________________________ .sup.a Scanner
used in Examples II & III. .sup.b 450 nm erase lamp cutoff
filter used. .sup.c No erase lamp cutoff filter used.
The V.sub.r cycle-up associated with the erase lamp cutoff filter
was again observed to occur and then disappear when the same device
was tested in the motionless scanner without the erase lamp cutoff
filter for 3000 cycles. Although this device was not peel tested,
acceptable adhesion is anticipated with delamination probably
occurring at the titanium conductive layer-blocking layer interface
(as described for the first device in this Example) since the
blocking layer-generating layer interfacial adhesion is known to be
large (Example II, Table I, Device No. 2).
Although the invention has been described with reference to
specific preferred embodiments, it is not intended to be limited
thereto, rather those skilled in the art will recognize that
variations and modifications may be made therein which are within
the spirit of the invention and within the scope of the claims.
* * * * *